fix: type the ids filter from its configured id type

advanced_alchemy annotates the `ids` query parameter as list[str] whatever the
config says, so a bigint primary key was compared against strings and Postgres
refused. Nothing had called ?ids= until now.

backend/tests/integration/test_book.py

@@ -209,6 +209,21 @@ async def test_get_book_file(
     assert downloaded_content == file_content
 
 
+async def test_list_books_by_id(populated_authenticated_client: AsyncClient) -> None:
+    """
+    `?ids=` has to reach the database as integers.
+
+    advanced_alchemy's stock id filter annotates the parameter as `list[str]` whatever
+    the configured id type, so the ids arrived as strings and Postgres refused to
+    compare a bigint primary key against them. Nothing called it until a screen needed
+    to fetch a handful of books by id.
+    """
+    response = await populated_authenticated_client.get("/books?ids=1&ids=2&pageSize=10")
+
+    assert response.status_code == 200
+    assert sorted(book["id"] for book in response.json()["items"]) == [1, 2]
+
+
 async def test_get_book_by_id(populated_authenticated_client: AsyncClient) -> None:
     """Test retrieving a specific book by ID."""