refactor: replace SQLModel with QueryModel in various models and update query methods

backend/app/models/base.py

@@ -0,0 +1,11 @@
+from __future__ import annotations
+
+from typing import ClassVar, Self
+
+from sqlmodel import SQLModel
+
+from app.db.query_manager import ManagerDescriptor
+
+
+class QueryModel(SQLModel, table=False):
+    objects: ClassVar[ManagerDescriptor[Self]] = ManagerDescriptor()