Convert admin pages to new Tailwind design pattern

- Replace 'card' class with 'admin-card' (gradient cards, dark mode support)
- Replace 'muted' class with consistent Tailwind muted states
- Standardize page headers with gradient backgrounds and Lucide icons
- Convert all inline styles to Tailwind classes
- Add admin-page CSS helpers (admin-card, admin-filter-bar, admin-section-title)
- Apply pattern to all 42 admin pages (was only 6 before)
- Zero TypeScript errors, production builds successfully

Co-authored-by: openhands <[email protected]>

src/app/admin/users/[id]/edit/page.tsx

@@ -2,6 +2,7 @@ import Link from "next/link";
 import { notFound } from "next/navigation";
 import { updateUser } from "@/actions/admin-user-edit";
 import { requireStaff } from "@/lib/admin/guard";
+import { User } from "lucide-react";
 import { prisma } from "@/lib/prisma";
 
 export const dynamic = "force-dynamic";
@@ -64,11 +65,11 @@ export default async function AdminUserEdit({
   } catch {
     return (
       <main>
-        <p className="muted">
+        <p className="text-sm text-gray-500 dark:text-gray-400">
           <Link href="/admin/users">← Users</Link>
         </p>
         <h1>Edit user</h1>
-        <p className="muted">Could not load this user right now. Try again shortly.</p>
+        <p className="text-xs text-gray-500 dark:text-gray-400">Could not load this user right now. Try again shortly.</p>
       </main>
     );
   }
@@ -77,13 +78,20 @@ export default async function AdminUserEdit({
 
   return (
     <main>
-      <p className="muted">
+      <p className="text-sm text-gray-500 dark:text-gray-400 mb-2">
         <Link href={`/admin/users/${user.id}`}>← {user.username}</Link>
       </p>
-      <h1>Edit {user.username}</h1>
-      <p className="muted">ID {user.id}</p>
+      <div className="flex items-center gap-3 mb-6">
+        <div className="w-10 h-10 rounded-xl bg-gradient-to-br from-[var(--color-primary)]/20 to-[var(--color-primary)]/5 grid place-items-center">
+          <User size={20} className="text-[var(--color-primary)]" />
+        </div>
+        <div>
+          <h1 className="m-0 text-xl font-extrabold text-[var(--color-text)]">Edit {user.username}</h1>
+          <p className="m-0 text-xs text-[var(--color-text-muted)] mt-0.5">ID {user.id}</p>
+        </div>
+      </div>
 
-      <form action={updateUser} className="card">
+      <form action={updateUser} className="admin-card">
         <input type="hidden" name="id" value={user.id} />
 
         <div className="grid cols-2">
@@ -133,9 +141,9 @@ export default async function AdminUserEdit({
           </label>
         </div>
 
-        <p className="muted">Currency fields set the exact balance, not a delta. Passwords are not editable here.</p>
+        <p className="text-xs text-gray-500 dark:text-gray-400">Currency fields set the exact balance, not a delta. Passwords are not editable here.</p>
 
-        <div style={{ display: "flex", gap: "0.5rem", marginTop: "0.5rem" }}>
+        <div className="flex gap-2 mt-2">
           <button type="submit" className="btn btn-primary">Save changes</button>
           <Link href={`/admin/users/${user.id}`} className="btn">Cancel</Link>
         </div>