fix(artist): ruff UP017 + test_directory_card_shape pin

Two CI bounces on b65e956:
1. ruff UP017 — Python 3.14's preferred form is `datetime.UTC`, not
   `timezone.utc`. Switch the test's two TZ literals.
2. test_directory_card_shape pinned the card key set to the pre-feature
   shape; `unseen_count` was added to the API payload but the pin
   wasn't updated. Same shape as the recurring 'plan-grep-pinned-tests'
   trap — should have grepped tests/ for card.keys() before pushing.

tests/test_api_artists_directory.py

@@ -43,7 +43,8 @@ async def test_directory_card_shape(client, seeded):
     body = await resp.get_json()
     card = next(c for c in body["cards"] if c["name"] == "alice-api")
     assert set(card.keys()) == {
-        "id", "name", "slug", "is_subscription", "image_count", "preview_thumbnails",
+        "id", "name", "slug", "is_subscription", "image_count",
+        "unseen_count", "preview_thumbnails",
     }
     assert card["is_subscription"] is True
     assert card["image_count"] == 1