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/subscriptions/page.tsx

@@ -52,7 +52,7 @@ export default async function AdminSubscriptions() {
         Active Habbo Club / VIP subscriptions (expiry > now). 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="Active subs" value={active.length} icon="⭐" />
         <StatusCard label="Types" value={types} icon="🏷️" />
         <StatusCard
@@ -63,7 +63,7 @@ export default async function AdminSubscriptions() {
         />
       </div>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Active subscriptions ({active.length})</h2>
         <div className="card">
           <table>
@@ -85,7 +85,7 @@ export default async function AdminSubscriptions() {
                     <td>{s.userId ?? "—"}</td>
                     <td>{s.subscriptionType ?? "—"}</td>
                     <td>
-                      <span className={`admin-badge ${soon ? "" : "ok"}`}>
+                      <span className={`inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full ${soon ? "bg-[var(--color-primary)]/18 text-[var(--color-text)]" : "bg-green-600/20 text-[var(--color-text)]"}`}>
                         {soon ? "Expiring" : "Active"}
                       </span>
                     </td>