feat: redesign admin panel with Lucide icons and modern styling

- Add lucide-react for SVG icons throughout the admin
- Redesign sidebar with gradient background, icons per nav item, and sticky layout
- Redesign topbar with cleaner user info display
- Redesign dashboard with icon-backed stat cards, gradient progress bars, activity feed
- Update AdminNavLink with icon support and new active state styling
- Improve table styling in admin-page CSS (rounded corners, hover, spacing)
- Clean up unused admin CSS

src/components/admin/dashboard.tsx

@@ -25,26 +25,20 @@ export function StatusCard({
   value: ReactNode;
   hint?: string;
   state?: State;
-  icon?: string;
+  icon?: ReactNode;
 }) {
-  const borderColor =
-    state === "ok" ? "border-l-green-600" :
-    state === "warn" ? "border-l-[var(--color-primary)]" :
-    state === "danger" ? "border-l-red-500" :
-    "border-l-[var(--color-text-muted)]";
-
   return (
-    <div className={`bg-[var(--color-surface)] border border-[var(--border)] border-l-4 ${borderColor} rounded-xl p-3.5 shadow-card`}>
-      <div className="flex items-center justify-between gap-2">
-        <span className="text-[0.72rem] font-bold uppercase tracking-wider text-[var(--color-text-muted)]">{label}</span>
+    <div className="bg-[var(--color-surface)] border border-[var(--border)] rounded-2xl p-5 shadow-card hover:shadow-card-hover transition-shadow duration-200">
+      <div className="flex items-center justify-between gap-3 mb-3">
+        <span className="text-[0.65rem] font-bold uppercase tracking-widest text-[var(--color-text-muted)]">{label}</span>
         {icon ? (
-          <span className="text-lg leading-none" aria-hidden>
+          <span className="w-8 h-8 rounded-xl bg-gradient-to-br from-[var(--color-primary)]/15 to-[var(--color-primary)]/5 grid place-items-center text-[var(--color-primary)] flex-none">
             {icon}
           </span>
         ) : null}
       </div>
-      <div className="text-[1.7rem] font-extrabold leading-tight mt-1.5">{value}</div>
-      {hint ? <div className="text-[0.78rem] text-[var(--color-text-muted)] mt-1">{hint}</div> : null}
+      <div className="text-2xl font-extrabold text-[var(--color-text)] leading-tight">{value}</div>
+      {hint ? <div className="text-[0.7rem] text-[var(--color-text-muted)] mt-1.5 font-medium">{hint}</div> : null}
     </div>
   );
 }