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/emulator/page.tsx

@@ -41,12 +41,12 @@ export default async function AdminEmulator() {
         on the next emulator read (some keys require an emulator reload).
       </p>
 
-      <div className="admin-stats">
+      <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
         <StatusCard label="Settings keys" value={settings.length} icon="⚙️" />
         <StatusCard label="Text keys" value={textsCount} icon="🗒️" />
       </div>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Settings</h2>
         <p className="muted" style={{ marginTop: "-0.4rem" }}>
           {settings.length} keys.
@@ -111,7 +111,7 @@ export default async function AdminEmulator() {
       ) : null}
       </section>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Texts</h2>
         <p className="muted" style={{ marginTop: "-0.4rem" }}>
           {textsCount} keys{textsTruncated ? ` (showing first ${texts.length})` : ""}.