feat: add user role field and implement Gravatar fallback for user avatars

apps/backend/src/modules/user/services/user.service.ts

@@ -1,13 +1,19 @@
+import { createHash } from 'node:crypto';
 import type { User } from '@/lib/auth';
 import type { UserProfile } from '@repo/api-contract';
 
+function getGravatarUrl(email: string): string {
+  const hash = createHash('md5').update(email.trim().toLowerCase()).digest('hex');
+  return `https://www.gravatar.com/avatar/${hash}?d=identicon`;
+}
+
 export function getUserProfile(user: User): UserProfile {
   return {
     id: user.id,
     fullName: user.name,
     email: user.email,
     role: (user as any).role || 'member',
-    avatarUrl: user.image || null,
+    avatarUrl: user.image || getGravatarUrl(user.email),
     createdAt: user.createdAt,
   };
 }