refactor: convert admin panel to Tailwind CSS

- Convert admin layout, sidebar, and navigation to Tailwind classes
- Convert dashboard components (StatusCard, DiagnosticRow, etc.) to Tailwind
- Convert all ~48 admin page files from admin CSS classes to Tailwind
- Remove unused admin CSS from globals.css (973 → 712 lines)
- Convert developers page badges to Tailwind
- Remove <style jsx> block from OnlineUsersWidget

src/app/admin/catalog/page.tsx

@@ -53,7 +53,7 @@ export default async function AdminCatalog() {
         Browse catalog pages and the items they contain. Read-only.
       </p>
 
-      <div className="admin-stats">
+      <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
         <StatusCard label="Pages" value={pages.length} icon="📚" />
         <StatusCard label="Visible" value={visibleCount} state="ok" icon="👁️" />
         <StatusCard
@@ -65,7 +65,7 @@ export default async function AdminCatalog() {
         <StatusCard label="Root pages" value={rootCount} icon="🗂️" />
       </div>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Pages ({pages.length})</h2>
         {pages.length === 0 ? (
           <p className="muted">No catalog pages found.</p>
@@ -105,7 +105,7 @@ export default async function AdminCatalog() {
                       <td>{p.minRank}</td>
                       <td>{p.orderNum}</td>
                       <td>
-                        <span className={`admin-badge ${hidden ? "danger" : "ok"}`}>
+                        <span className={`inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full ${hidden ? "bg-red-500/22 text-[var(--color-text)]" : "bg-green-600/20 text-[var(--color-text)]"}`}>
                           {hidden ? "Hidden" : "Visible"}
                         </span>
                       </td>