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/radio/points/page.tsx

@@ -66,7 +66,7 @@ export default async function AdminRadioPointsPage({
         <Link href="/admin/radio/history">History</Link>
       </nav>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Radio Listener Points</h2>
         <p className="muted" style={{ marginTop: "-0.4rem" }}>
           Reward listeners with currency for time spent on the radio. Edits write
@@ -77,11 +77,11 @@ export default async function AdminRadioPointsPage({
 
         {saved === "1" ? (
           <p>
-            <span className="admin-badge ok">Saved</span>
+            <span className="inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full bg-green-600/20 text-[var(--color-text)]">Saved</span>
           </p>
         ) : null}
 
-        <div className="admin-stats">
+        <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
           <StatusCard
             label="Points"
             value={enabled ? "Enabled" : "Disabled"}
@@ -103,7 +103,7 @@ export default async function AdminRadioPointsPage({
         </div>
       </section>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Settings</h2>
         <form action={savePoints}>
           <div className="grid cols-2">