refactor(backend): refactor project, add database migrations support

backend/app/services/db.py

@@ -0,0 +1,14 @@
+from typing import AsyncGenerator
+from fastapi import Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+from fastapi_users.db import SQLAlchemyUserDatabase
+
+from ..core.db import async_session_maker
+from ..models.user import User
+
+async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
+    async with async_session_maker() as session:
+        yield session
+
+async def get_user_db(session: AsyncSession = Depends(get_async_session)):
+    yield SQLAlchemyUserDatabase(session, User)