test: lock that the deck list omits cards (#58)

Port the regression test from litestar-sqlalchemy-template#33. The Deck
response contract is two-shaped: light `Deck` for list/create/update,
`DeckWithCards` for get_deck. No test asserted that `cards` is absent
from list responses, so the contract wasn't pinned — the existing tests
passed under both the old single-schema design and the split.

test_list_decks_omits_cards creates a deck with a card, then asserts the
list item has no `cards` key. It would catch a regression that re-added
`cards` to the light contract. test_get_one_deck already locks the other
half (detail includes cards).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lesnik512

tests/test_decks.py

@@ -35,6 +35,16 @@ async def test_get_decks(client: AsyncClient) -> None:
         assert v == getattr(deck, k)
 
 
+async def test_list_decks_omits_cards(client: AsyncClient) -> None:
+    deck = await factories.DeckModelFactory.create_async()
+    await factories.CardModelFactory.create_async(deck_id=deck.id)
+
+    response = await client.get("/api/decks/")
+    assert response.status_code == status.HTTP_200_OK
+    item = response.json()["items"][0]
+    assert "cards" not in item
+
+
 async def test_get_one_deck(client: AsyncClient) -> None:
     deck = await factories.DeckModelFactory.create_async()
     card = await factories.CardModelFactory.create_async(deck_id=deck.id)