Delegate user persistence to UserRepository

- Add create() and update() methods to UserRepository
- Update ProfileService to use repository.update()
- Update AuthService to use repository.create()

backend/services/profile.py

@@ -68,8 +68,7 @@ class ProfileService:
         user.signal = data.signal
         user.nostr_npub = data.nostr_npub
 
-        await self.db.commit()
-        await self.db.refresh(user)
+        await self.user_repo.update(user)
 
         godfather_email = await self.user_repo.get_godfather_email(user.godfather_id)