Add admin CMS Settings editor (website_settings)

/admin/settings: list all website_settings, inline value edit, add/overwrite,
delete; staff-gated server actions that bust the siteSettings cache after each
write. Admin nav extended (Settings).

Verified: tsc exit 0, vitest 48/48, next build exit 0.

src/actions/admin-settings.ts

@@ -0,0 +1,40 @@
+"use server";
+
+import { revalidatePath } from "next/cache";
+import { requireStaff } from "@/lib/admin/guard";
+import { prisma } from "@/lib/prisma";
+import { siteSettings } from "@/lib/services/site-settings";
+
+export async function updateSetting(formData: FormData): Promise<void> {
+  await requireStaff();
+  const key = String(formData.get("key") ?? "").trim();
+  const value = String(formData.get("value") ?? "");
+  if (!key) return;
+  await prisma.websiteSetting.update({ where: { key }, data: { value } });
+  siteSettings.reload();
+  revalidatePath("/admin/settings");
+}
+
+export async function createSetting(formData: FormData): Promise<void> {
+  await requireStaff();
+  const key = String(formData.get("key") ?? "").trim().slice(0, 255);
+  const value = String(formData.get("value") ?? "");
+  const comment = String(formData.get("comment") ?? "").trim().slice(0, 255);
+  if (!key) return;
+  await prisma.websiteSetting.upsert({
+    where: { key },
+    update: { value },
+    create: { key, value, comment: comment || null },
+  });
+  siteSettings.reload();
+  revalidatePath("/admin/settings");
+}
+
+export async function deleteSetting(formData: FormData): Promise<void> {
+  await requireStaff();
+  const key = String(formData.get("key") ?? "").trim();
+  if (!key) return;
+  await prisma.websiteSetting.delete({ where: { key } });
+  siteSettings.reload();
+  revalidatePath("/admin/settings");
+}

src/app/admin/layout.tsx

@@ -18,6 +18,7 @@ export default async function AdminLayout({ children }: { children: ReactNode })
           <Link href="/admin/users">Users</Link>
           <Link href="/admin/articles">Articles</Link>
           <Link href="/admin/bans">Bans</Link>
+          <Link href="/admin/settings">Settings</Link>
         </nav>
       </aside>
       <section>{children}</section>

src/app/admin/settings/page.tsx

@@ -0,0 +1,55 @@
+import { createSetting, deleteSetting, updateSetting } from "@/actions/admin-settings";
+import { prisma } from "@/lib/prisma";
+
+export const dynamic = "force-dynamic";
+
+export default async function AdminSettings() {
+  const settings = await prisma.websiteSetting.findMany({ orderBy: { key: "asc" } });
+
+  return (
+    <main>
+      <h1>CMS Settings</h1>
+      <p className="muted">
+        Key/value config read at runtime via <code>siteSettings.get()</code>. Saving busts the cache.
+      </p>
+
+      <form action={createSetting} className="card" style={{ marginBottom: "1.5rem" }}>
+        <h3 style={{ marginTop: 0 }}>Add / overwrite</h3>
+        <div style={{ display: "flex", gap: "0.5rem", flexWrap: "wrap" }}>
+          <input name="key" placeholder="key" required />
+          <input name="value" placeholder="value" style={{ flex: 1, minWidth: 160 }} />
+          <input name="comment" placeholder="comment" />
+          <button type="submit">Save</button>
+        </div>
+      </form>
+
+      <div className="grid">
+        {settings.map((s) => (
+          <div key={s.key} className="card">
+            <div style={{ display: "flex", gap: "0.75rem", alignItems: "baseline" }}>
+              <strong style={{ minWidth: 220 }}>{s.key}</strong>
+              <form
+                action={updateSetting}
+                style={{ display: "flex", gap: "0.5rem", flex: 1 }}
+              >
+                <input type="hidden" name="key" value={s.key} />
+                <input name="value" defaultValue={s.value} style={{ flex: 1 }} />
+                <button type="submit">Save</button>
+              </form>
+              <form action={deleteSetting}>
+                <input type="hidden" name="key" value={s.key} />
+                <button type="submit">✕</button>
+              </form>
+            </div>
+            {s.comment ? (
+              <p className="muted" style={{ margin: "0.4rem 0 0" }}>
+                {s.comment}
+              </p>
+            ) : null}
+          </div>
+        ))}
+      </div>
+      {settings.length === 0 ? <p className="muted">No settings yet.</p> : null}
+    </main>
+  );
+}