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/housekeeping/page.tsx

@@ -49,13 +49,13 @@ export default async function AdminHousekeeping({
         existing key overwrites its min rank and description.
       </p>
 
-      <div className="admin-stats">
+      <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
         <StatusCard label="Permissions" value={permissions.length} icon="🔑" />
         <StatusCard label="Highest min rank" value={maxRank} icon="⬆️" />
         <StatusCard label="Total min rank" value={totalMin} icon="∑" />
       </div>
 
-      <div className="card admin-section-header" style={{ marginBottom: "1rem" }}>
+      <div className="card mt-6" style={{ marginBottom: "1rem" }}>
         <div style={{ display: "flex", gap: "0.5rem", alignItems: "center", flexWrap: "wrap" }}>
           <form style={{ display: "flex", gap: "0.5rem", flex: 1 }}>
             <input
@@ -97,7 +97,7 @@ export default async function AdminHousekeeping({
       </div>
 
       {mode === "manage" ? (
-        <section className="admin-section">
+        <section className="mt-6">
           <h2>Add / overwrite permission</h2>
           <form action={upsertPermission} className="card">
             <div style={{ display: "flex", gap: "0.5rem", flexWrap: "wrap" }}>
@@ -109,7 +109,7 @@ export default async function AdminHousekeeping({
           </form>
         </section>
       ) : (
-        <section className="admin-section">
+        <section className="mt-6">
           <h2>Import Permissions</h2>
           <p className="muted" style={{ marginTop: "-0.4rem" }}>
             Paste comma-separated permission IDs to import them as a selection.
@@ -123,9 +123,9 @@ export default async function AdminHousekeeping({
         </section>
       )}
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>
-          Permissions <span className="admin-badge">{filtered.length}</span>
+          Permissions <span className="inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full bg-[var(--color-primary)]/18 text-[var(--color-text)]">{filtered.length}</span>
         </h2>
         {filtered.length === 0 ? (
           <p className="muted">No housekeeping permissions match this search.</p>