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/logs/page.tsx

@@ -86,7 +86,7 @@ export default async function AdminStaffActivities({
         Auditor trail of all staff actions in the hotel.
       </p>
 
-      <div className="admin-stats">
+      <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
         <StatusCard label="Total activities" value={total} icon="📋" />
         <StatusCard label="On this page" value={activities.length} icon="📄" />
         <StatusCard
@@ -130,7 +130,7 @@ export default async function AdminStaffActivities({
         )}
       </form>
 
-      <section className="admin-section">
+      <section className="mt-6">
         <h2>Activities ({total})</h2>
         {activities.length === 0 ? (
           <p className="muted">No staff activities match this search.</p>
@@ -153,7 +153,7 @@ export default async function AdminStaffActivities({
                     <td className="muted" style={{ whiteSpace: "nowrap" }}>{fromDate(a.createdAt)}</td>
                     <td className="muted">#{Number(a.userId)} ({nameById.get(Number(a.userId)) ?? "unknown"})</td>
                     <td>
-                      <span className="admin-badge">{a.action}</span>
+                      <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)]">{a.action}</span>
                     </td>
                     <td>{a.description}</td>
                     <td>