Add live contrast preview to theme editor for guaranteed readability

- New client ColorField component shows a live 'Aa' text preview on the
  relevant background and a WCAG contrast ratio badge (✓ / ⚠)
- Flags low-contrast (<4.5:1) text fields with a red border and a
  one-click 'Use readable color' fix
- Map each text color to the background it sits on (body text -> surface,
  button text -> button color, navbar text -> navbar, admin text -> canvas)

src/app/admin/theme/color-field.tsx

@@ -0,0 +1,138 @@
+"use client";
+
+import { useState } from "react";
+
+interface Field {
+  key: string;
+  label: string;
+  def: string;
+  desc: string;
+  bgKey?: string;
+}
+
+function hexToRgb(hex: string): readonly [number, number, number] | null {
+  const m = /^#([0-9a-f]{6})$/i.exec(hex.trim());
+  if (!m) return null;
+  const n = Number.parseInt(m[1], 16);
+  return [(n >> 16) & 255, (n >> 8) & 255, n & 255];
+}
+
+function luminance([r, g, b]: readonly [number, number, number]): number {
+  const a = [r, g, b].map((v) => {
+    const c = v / 255;
+    return c <= 0.04045 ? c / 12.92 : ((c + 0.055) / 1.055) ** 2.4;
+  });
+  return 0.2126 * a[0] + 0.7152 * a[1] + 0.0722 * a[2];
+}
+
+function contrastRatio(a: string, b: string): number | null {
+  const ra = hexToRgb(a);
+  const rb = hexToRgb(b);
+  if (!ra || !rb) return null;
+  const l1 = luminance(ra);
+  const l2 = luminance(rb);
+  const hi = Math.max(l1, l2);
+  const lo = Math.min(l1, l2);
+  return (hi + 0.05) / (lo + 0.05);
+}
+
+function readableOn(bg: string): string {
+  const black = contrastRatio("#000000", bg) ?? 0;
+  const white = contrastRatio("#ffffff", bg) ?? 0;
+  return white >= black ? "#ffffff" : "#000000";
+}
+
+export function ColorField({
+  field,
+  value,
+  bgValue,
+  name,
+}: {
+  field: Field;
+  value: string;
+  bgValue?: string;
+  name: string;
+}) {
+  const [val, setVal] = useState(value);
+  const ratio = bgValue ? contrastRatio(val, bgValue) : null;
+  const poor = ratio != null && ratio < 4.5;
+  const ok = ratio != null && ratio >= 4.5;
+
+  return (
+    <div
+      style={{
+        display: "flex",
+        gap: "0.6rem",
+        padding: "0.5rem",
+        borderRadius: 8,
+        border: poor ? "1px solid #ef4444" : "1px solid transparent",
+        background: poor ? "rgba(239,68,68,0.08)" : "transparent",
+      }}
+    >
+      <input
+        type="color"
+        name={name}
+        value={val}
+        onChange={(e) => setVal(e.target.value)}
+        style={{ width: 42, height: 36, padding: 0, border: "none", background: "none", cursor: "pointer", flexShrink: 0 }}
+      />
+      <div style={{ display: "flex", flexDirection: "column", minWidth: 0, flex: 1 }}>
+        <div style={{ display: "flex", justifyContent: "space-between", alignItems: "baseline", gap: "0.5rem" }}>
+          <span style={{ fontSize: "0.82rem", fontWeight: 600, lineHeight: 1.2 }}>{field.label}</span>
+          {ratio != null ? (
+            <span style={{ fontSize: "0.7rem", fontWeight: 700, color: ok ? "#22c55e" : "#ef4444", whiteSpace: "nowrap" }}>
+              {ratio.toFixed(1)}:1 {ok ? "✓" : "⚠"}
+            </span>
+          ) : null}
+        </div>
+        <span
+          style={{
+            fontSize: "0.7rem",
+            color: "var(--admin-text-muted)",
+            lineHeight: 1.3,
+            display: "-webkit-box",
+            WebkitLineClamp: 2,
+            WebkitBoxOrient: "vertical",
+            overflow: "hidden",
+          }}
+        >
+          {field.desc}
+        </span>
+        {bgValue ? (
+          <div
+            style={{
+              marginTop: 4,
+              padding: "2px 8px",
+              borderRadius: 4,
+              background: bgValue,
+              color: val,
+              fontSize: "0.75rem",
+              fontWeight: 600,
+            }}
+          >
+            Aa Text preview
+          </div>
+        ) : null}
+        {poor && bgValue ? (
+          <button
+            type="button"
+            onClick={() => setVal(readableOn(bgValue))}
+            style={{
+              marginTop: 4,
+              alignSelf: "flex-start",
+              fontSize: "0.7rem",
+              fontWeight: 600,
+              color: "var(--admin-accent)",
+              background: "none",
+              border: "none",
+              padding: 0,
+              cursor: "pointer",
+            }}
+          >
+            Use readable color →
+          </button>
+        ) : null}
+      </div>
+    </div>
+  );
+}

src/app/admin/theme/page.tsx

@@ -2,18 +2,19 @@ import { getTranslations } from "next-intl/server";
 import { applyPreset, saveTheme } from "@/actions/admin-theme";
 import { siteSettings } from "@/lib/services/site-settings";
 import { FONTS, PRESETS } from "@/lib/theme-presets";
+import { ColorField } from "./color-field";
 
 export const dynamic = "force-dynamic";
 export const metadata = { title: "Theme" };
 
-const COLOR_FIELDS: { key: string; label: string; def: string; desc: string }[] = [
+const COLOR_FIELDS: { key: string; label: string; def: string; desc: string; bgKey?: string }[] = [
   { key: "color_background", label: "Page background", def: "#f8fafc", desc: "Main page background behind all content" },
   { key: "color_surface", label: "Card / surface", def: "#ffffff", desc: "Cards, panels, and elevated surfaces" },
   { key: "color_dropdown", label: "Dropdown menu", def: "#ffffff", desc: "Dropdown menus and input backgrounds" },
   { key: "color_navbar", label: "Navbar bar", def: "#ffffff", desc: "Top navigation bar background" },
-  { key: "color_navbar_text", label: "Navbar text", def: "#1e293b", desc: "Text color in the navigation bar" },
-  { key: "color_text", label: "Body text", def: "#0f172a", desc: "Main body text — must contrast with background/surface" },
-  { key: "color_text_muted", label: "Muted text", def: "#64748b", desc: "Secondary text, labels, hints — lighter than body text" },
+  { key: "color_navbar_text", label: "Navbar text", def: "#1e293b", desc: "Text color in the navigation bar", bgKey: "color_navbar" },
+  { key: "color_text", label: "Body text", def: "#0f172a", desc: "Main body text — must contrast with background/surface", bgKey: "color_surface" },
+  { key: "color_text_muted", label: "Muted text", def: "#64748b", desc: "Secondary text, labels, hints — lighter than body text", bgKey: "color_surface" },
   { key: "color_primary", label: "Primary accent", def: "#f59e0b", desc: "Main brand color, highlights, active elements" },
   { key: "color_accent", label: "Secondary accent", def: "#10b981", desc: "Secondary brand color, success-oriented highlights" },
   { key: "border_color", label: "Border (golden)", def: "#eeb425", desc: "Borders, dividers, outlines" },
@@ -23,17 +24,17 @@ const COLOR_FIELDS: { key: string; label: string; def: string; desc: string }[]
   { key: "color_info", label: "Info", def: "#0ea5e9", desc: "Info status (blue)" },
 ];
 
-const BUTTON_FIELDS: { key: string; label: string; def: string; desc: string }[] = [
+const BUTTON_FIELDS: { key: string; label: string; def: string; desc: string; bgKey?: string }[] = [
   { key: "button_primary_color", label: "Primary button", def: "#f59e0b", desc: "Main call-to-action button background" },
-  { key: "button_text_color", label: "Button text", def: "#1e293b", desc: "Text on primary buttons — must contrast with button color" },
+  { key: "button_text_color", label: "Button text", def: "#1e293b", desc: "Text on primary buttons — must contrast with button color", bgKey: "button_primary_color" },
   { key: "button_secondary_color", label: "Secondary button", def: "#22c55e", desc: "Secondary action button background" },
-  { key: "button_secondary_text_color", label: "Secondary text", def: "#ffffff", desc: "Text on secondary buttons" },
+  { key: "button_secondary_text_color", label: "Secondary text", def: "#ffffff", desc: "Text on secondary buttons", bgKey: "button_secondary_color" },
   { key: "button_danger_color", label: "Danger button", def: "#ef4444", desc: "Destructive action button (delete, ban)" },
-  { key: "button_danger_text_color", label: "Danger text", def: "#ffffff", desc: "Text on danger buttons" },
+  { key: "button_danger_text_color", label: "Danger text", def: "#ffffff", desc: "Text on danger buttons", bgKey: "button_danger_color" },
   { key: "button_outline_color", label: "Outline border", def: "#eeb425", desc: "Outline button border color" },
-  { key: "button_outline_text_color", label: "Outline text", def: "#1a1a2e", desc: "Text on outline buttons" },
-  { key: "link_color", label: "Link", def: "#eeb425", desc: "Hyperlink text color" },
-  { key: "link_hover_color", label: "Link hover", def: "#cf9d15", desc: "Hyperlink text on hover" },
+  { key: "button_outline_text_color", label: "Outline text", def: "#1a1a2e", desc: "Text on outline buttons", bgKey: "color_surface" },
+  { key: "link_color", label: "Link", def: "#eeb425", desc: "Hyperlink text color", bgKey: "color_surface" },
+  { key: "link_hover_color", label: "Link hover", def: "#cf9d15", desc: "Hyperlink text on hover", bgKey: "color_surface" },
 ];
 
 const GRADIENT_FIELDS: { key: string; label: string; def: string; desc: string }[] = [
@@ -47,11 +48,11 @@ const HEADINGS: { key: string; label: string; def: string }[] = [
   { key: "size_heading_h3", label: "H3", def: "18" },
 ];
 
-const ADMIN_FIELDS: { key: string; label: string; def: string; desc: string }[] = [
+const ADMIN_FIELDS: { key: string; label: string; def: string; desc: string; bgKey?: string }[] = [
   { key: "admin_canvas", label: "Page background", def: "#0f172a", desc: "Main admin page background" },
   { key: "admin_surface", label: "Card / panel", def: "#1e293b", desc: "Admin cards, tables, and panel backgrounds" },
-  { key: "admin_text", label: "Body text", def: "#f1f5f9", desc: "Main admin text — must contrast with canvas/surface" },
-  { key: "admin_text_muted", label: "Muted text", def: "#94a3b8", desc: "Secondary labels, hints, descriptions" },
+  { key: "admin_text", label: "Body text", def: "#f1f5f9", desc: "Main admin text — must contrast with canvas/surface", bgKey: "admin_canvas" },
+  { key: "admin_text_muted", label: "Muted text", def: "#94a3b8", desc: "Secondary labels, hints, descriptions", bgKey: "admin_canvas" },
   { key: "admin_border", label: "Border", def: "#334155", desc: "Table borders, dividers, input outlines" },
   { key: "admin_sidebar_bg", label: "Sidebar", def: "#0f172a", desc: "Left navigation sidebar background" },
 ];
@@ -67,13 +68,13 @@ interface ThemeField {
   label: string;
   def: string;
   desc: string;
+  bgKey?: string;
 }
 
-function colorGrid(
+function colorFields(
   fields: ThemeField[],
   current: Record<string, string>,
   suffix = "",
-  bgHint?: string,
 ) {
   return (
     <div
@@ -85,30 +86,16 @@ function colorGrid(
     >
       {fields.map((f) => {
         const val = toHex(current[f.key], f.def);
+        const bgKey = f.bgKey ? `${f.bgKey}${suffix}` : undefined;
+        const bgValue = bgKey ? toHex(current[bgKey], "") : undefined;
         return (
-          <div
+          <ColorField
             key={f.key}
-            style={{
-              display: "flex",
-              alignItems: "center",
-              gap: "0.6rem",
-              padding: "0.4rem 0.5rem",
-              borderRadius: 6,
-            }}
-          >
-            <input
-              type="color"
-              name={`${f.key}${suffix}`}
-              defaultValue={val}
-              style={{ width: 40, height: 32, padding: 0, border: "none", background: "none", cursor: "pointer", flexShrink: 0 }}
-            />
-            <div style={{ display: "flex", flexDirection: "column", minWidth: 0, flex: 1 }}>
-              <span style={{ fontSize: "0.82rem", fontWeight: 600, lineHeight: 1.3 }}>{f.label}</span>
-              <span style={{ fontSize: "0.7rem", color: "var(--admin-text-muted)", lineHeight: 1.3, display: "-webkit-box", WebkitLineClamp: 2, WebkitBoxOrient: "vertical", overflow: "hidden" }}>
-                {f.desc}
-              </span>
-            </div>
-          </div>
+            field={f}
+            value={val}
+            bgValue={bgValue || undefined}
+            name={`${f.key}${suffix}`}
+          />
         );
       })}
     </div>
@@ -218,7 +205,7 @@ export default async function AdminTheme({
           <p className="text-xs text-[var(--admin-text-muted)] mb-2">
             Backgrounds, surfaces, and text colors. Text colors must contrast with their backgrounds for readability.
           </p>
-          <div className="admin-card">{colorGrid(COLOR_FIELDS, current)}</div>
+          <div className="admin-card">{colorFields(COLOR_FIELDS, current)}</div>
         </section>
 
         <section className="mt-6">
@@ -226,7 +213,7 @@ export default async function AdminTheme({
           <p className="text-xs text-[var(--admin-text-muted)] mb-2">
             Button backgrounds, text on buttons, and link colors. Button text must contrast with its button background.
           </p>
-          <div className="admin-card">{colorGrid(BUTTON_FIELDS, current)}</div>
+          <div className="admin-card">{colorFields(BUTTON_FIELDS, current)}</div>
         </section>
 
         <section className="mt-6">
@@ -234,7 +221,7 @@ export default async function AdminTheme({
           <p className="text-xs text-[var(--admin-text-muted)] mb-2">
             Card header and hero section gradient. These blend from start → end across headings and banners.
           </p>
-          <div className="admin-card">{colorGrid(GRADIENT_FIELDS, current)}</div>
+          <div className="admin-card">{colorFields(GRADIENT_FIELDS, current)}</div>
         </section>
 
         <h2 className="mt-8 text-lg font-extrabold">🛠 Admin panel (HK)</h2>
@@ -243,7 +230,7 @@ export default async function AdminTheme({
           use auto-derived defaults.
         </p>
         <section className="mt-4">
-          <div className="admin-card">{colorGrid(ADMIN_FIELDS, current)}</div>
+          <div className="admin-card">{colorFields(ADMIN_FIELDS, current)}</div>
         </section>
 
         <h2 className="mt-8 text-lg font-extrabold">🌙 Dark mode</h2>
@@ -252,15 +239,15 @@ export default async function AdminTheme({
         </p>
         <section className="mt-4">
           <h3 className="admin-section-title">Page &amp; text colors</h3>
-          <div className="admin-card">{colorGrid(COLOR_FIELDS, currentDark, "_dark")}</div>
+          <div className="admin-card">{colorFields(COLOR_FIELDS, currentDark, "_dark")}</div>
         </section>
         <section className="mt-6">
           <h3 className="admin-section-title">Buttons &amp; links</h3>
-          <div className="admin-card">{colorGrid(BUTTON_FIELDS, currentDark, "_dark")}</div>
+          <div className="admin-card">{colorFields(BUTTON_FIELDS, currentDark, "_dark")}</div>
         </section>
         <section className="mt-6">
           <h3 className="admin-section-title">Gradients</h3>
-          <div className="admin-card">{colorGrid(GRADIENT_FIELDS, currentDark, "_dark")}</div>
+          <div className="admin-card">{colorFields(GRADIENT_FIELDS, currentDark, "_dark")}</div>
         </section>
 
         <section className="mt-6">