feat: roles/permissions system and Nostr profile display on admin users

Introduce granular role-based permissions with SuperAdmin env override, admin roles UI, and permission-gated API routes. Fix admin user Nostr metadata by batching relay profile fetches, normalizing npub pubkeys to hex, and adding reusable NostrAvatar/useNostrProfile components.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/admin/page.tsx

@@ -6,7 +6,7 @@ import { useAuth } from "@/hooks/useAuth";
 import { LogIn } from "lucide-react";
 
 export default function AdminPage() {
-  const { user, loading, login } = useAuth();
+  const { user, loading, login, isSuperAdmin, permissions } = useAuth();
   const router = useRouter();
   const [error, setError] = useState("");
   const [loggingIn, setLoggingIn] = useState(false);
@@ -14,12 +14,12 @@ export default function AdminPage() {
   useEffect(() => {
     if (loading) return;
     if (!user) return;
-    if (user.role === "ADMIN" || user.role === "MODERATOR") {
+    if (isSuperAdmin || permissions.length > 0) {
       router.push("/admin/overview");
     } else {
       router.push("/dashboard");
     }
-  }, [user, loading, router]);
+  }, [user, loading, isSuperAdmin, permissions, router]);
 
   const handleLogin = async () => {
     setError("");