chore: run ty on tests/ and make the new ingest tests pass it

Stop excluding tests/ from the ty-check pre-commit hook so touched test files
are type-checked. Fix the new ingest tests under the now-active check:
- cast duck-typed JobContext / App test doubles to their declared types;
- narrow the gated Postgres fixture's str | None URL (pytest.skip isn't modelled
  as NoReturn by ty).

Pre-existing type issues in untouched test modules are unaffected (the hook
checks only changed files); they'll be cleaned as those files are next touched.

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

tests/integration/test_ingest_queue_postgres.py

@@ -57,6 +57,8 @@ def postgres_url() -> str:
             "`docker compose --profile postgres up -d postgres-test` and export "
             "TEST_DATABASE_URL=postgresql+asyncpg://mcp:mcp@localhost:5433/mcp"
         )
+    # pytest.skip raises, but ty doesn't model it as NoReturn — narrow explicitly.
+    assert url is not None
     if not _reachable(url):
         pytest.skip(f"Postgres at {url} is not reachable")
     return url