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/repositories/user.py

@@ -30,3 +30,31 @@ class UserRepository:
             select(User.email).where(User.id == godfather_id)
         )
         return result.scalar_one_or_none()
+
+    async def create(self, user: User) -> User:
+        """
+        Create a new user record.
+
+        Args:
+            user: User instance to persist
+
+        Returns:
+            Created User record (flushed to get ID)
+        """
+        self.db.add(user)
+        await self.db.flush()
+        return user
+
+    async def update(self, user: User) -> User:
+        """
+        Update an existing user record.
+
+        Args:
+            user: User instance to update
+
+        Returns:
+            Updated User record (refreshed from database)
+        """
+        await self.db.commit()
+        await self.db.refresh(user)
+        return user