feat(users): add get user by id endpoint

backend/src/v1/users/service.py

@@ -20,6 +20,7 @@ if TYPE_CHECKING:
     from sqlalchemy.ext.asyncio import AsyncSession
 
     from v1.auth.schemas import UserByEmailResponse
+    from v1.friendships.schemas import UserBasicInfo
 
 logger = get_logger("v1.users.service")
 
@@ -99,6 +100,22 @@ class UserService(BaseService):
             bio=user.bio,
         )
 
+    async def get_user_by_id(self, user_id: UUID) -> "UserBasicInfo":
+        from v1.friendships.schemas import UserBasicInfo
+
+        try:
+            profile = await self._repository.get_by_user_id(user_id)
+        except SQLAlchemyError:
+            raise HTTPException(status_code=503, detail="User store unavailable")
+
+        if profile is None:
+            raise HTTPException(status_code=404, detail="User not found")
+        return UserBasicInfo(
+            id=str(profile.id),
+            username=profile.username,
+            avatar_url=profile.avatar_url,
+        )
+
     async def update_me(self, update: UserUpdateRequest) -> UserResponse:
         user_id = self.require_user_id()
         update_data: dict[str, str | None] = {