chore: restructure project directory and update Dockerfile paths

app/core/mongodb.py

@@ -0,0 +1,24 @@
+from motor.motor_asyncio import AsyncIOMotorClient, AsyncIOMotorDatabase
+
+from core.config import settings
+
+
+class _MongoDB:
+    client: AsyncIOMotorClient | None = None
+
+    def get_database(self) -> AsyncIOMotorDatabase:
+        if self.client is None:
+            raise RuntimeError("MongoDB client has not been initialized")
+        return self.client[settings.MONGODB_DB_NAME]
+
+mongodb = _MongoDB()
+
+async def get_database() -> AsyncIOMotorDatabase:
+    return mongodb.get_database()
+
+
+async def ensure_mongodb_available() -> None:
+    client = mongodb.client
+    if client is None:
+        raise RuntimeError("MongoDB client has not been initialized")
+    await client.admin.command("ping")