refactor: update module docstrings for clarity and consistency

backend/app/db/pagination.py

@@ -1,14 +1,18 @@
+"""Typed wrapper around fastapi-pagination for backend query helpers."""
+
 from __future__ import annotations
 
 from collections.abc import Awaitable, Callable, Sequence
-from typing import Any, TypeVar, cast
+from typing import TYPE_CHECKING, Any, TypeVar, cast
 
 from fastapi_pagination.ext.sqlalchemy import paginate as _paginate
-from sqlmodel.ext.asyncio.session import AsyncSession
-from sqlmodel.sql.expression import Select, SelectOfScalar
 
 from app.schemas.pagination import DefaultLimitOffsetPage
 
+if TYPE_CHECKING:
+    from sqlmodel.ext.asyncio.session import AsyncSession
+    from sqlmodel.sql.expression import Select, SelectOfScalar
+
 T = TypeVar("T")
 
 Transformer = Callable[[Sequence[Any]], Sequence[Any] | Awaitable[Sequence[Any]]]
@@ -20,8 +24,10 @@ async def paginate(
     *,
     transformer: Transformer | None = None,
 ) -> DefaultLimitOffsetPage[T]:
-    # fastapi-pagination is not fully typed (it returns Any), but response_model validation
-    # ensures runtime correctness. Centralize casts here to keep strict mypy clean.
+    """Execute a paginated query and cast to the project page type alias."""
+    # fastapi-pagination is not fully typed (it returns Any), but response_model
+    # validation ensures runtime correctness. Centralize casts here to keep strict
+    # mypy clean.
     return cast(
         DefaultLimitOffsetPage[T],
         await _paginate(session, statement, transformer=transformer),