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/components/public/Navbar.tsx

@@ -80,7 +80,8 @@ export function Navbar() {
   }
 
   const displayName = user?.name || user?.displayName || shortenPubkey(user?.pubkey || "");
-  const isStaff = user?.role === "ADMIN" || user?.role === "MODERATOR";
+  const isStaff =
+    !!user?.isSuperAdmin || (user?.permissions?.length ?? 0) > 0;
 
   function handleLogout() {
     setDropdownOpen(false);