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/help-questions/page.tsx

@@ -33,13 +33,13 @@ export default async function AdminHelpQuestions() {
         the public help page, ordered by position.
       </p>
 
-      <div className="admin-stats">
+      <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
         <StatusCard label="Entries" value={entries.length} icon="❓" />
         <StatusCard label="With button" value={withButton} icon="🔘" />
         <StatusCard label="Small boxes" value={smallBoxes} icon="🗂️" />
       </div>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Entries</h2>
         {entries.length === 0 ? (
           <p className="muted">No help-center entries yet.</p>
@@ -63,7 +63,7 @@ export default async function AdminHelpQuestions() {
                   </td>
                   <td className="muted">{e.buttonText || "—"}</td>
                   <td>
-                    <span className={`admin-badge ${e.smallBox ? "ok" : ""}`}>
+                    <span className={`inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full ${e.smallBox ? "bg-green-600/20 text-[var(--color-text)]" : "bg-[var(--color-primary)]/18 text-[var(--color-text)]"}`}>
                       {e.smallBox ? "Yes" : "No"}
                     </span>
                   </td>