Fix admin redirect by using isAdmin from auth context instead of user_metadata.role

The root cause was that ProtectedRoute and Auth.tsx were checking user.user_metadata?.role,
but the admin role is stored in the user_roles table, not in user metadata.

Changes:
- ProtectedRoute: Use isAdmin flag from useAuth context instead of user.user_metadata?.role
- Auth.tsx: Use isAdmin flag for role-based redirect logic
- Remove redundant auth checks from individual admin/member pages (ProtectedRoute handles it)
- Add isAdmin to useEffect dependencies to ensure redirect happens after admin check completes

This fixes the issue where admins were being redirected to /dashboard instead of /admin
after login, because the role check was happening before the async admin role lookup completed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/pages/admin/AdminSettings.tsx

@@ -15,12 +15,6 @@ export default function AdminSettings() {
   const { user, isAdmin, loading: authLoading } = useAuth();
   const navigate = useNavigate();
 
-  useEffect(() => {
-    if (!authLoading) {
-      if (!user) navigate('/auth');
-      else if (!isAdmin) navigate('/dashboard');
-    }
-  }, [user, isAdmin, authLoading, navigate]);
 
   if (authLoading) {
     return (