fix: resolve mypy errors, fix arxiv test session isolation, and add premerge script

- Remove unused type:ignore comment in scholars.py
- Fix 51 mypy errors across test files (Any return types, cast(), protocol stubs)
- Fix arxiv unit test failures caused by session isolation (patch_session_factory fixture)
- Fix integration test rate-limit bleed between search and create
- Add scripts/premerge.sh for local CI verification
- Add docs/website/.docusaurus/ to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/unit/services/domains/arxiv/test_client.py

@@ -147,8 +147,8 @@ async def test_client_coalesces_concurrent_identical_search_requests() -> None:
 async def test_client_logs_cache_hit_and_miss(
     db_session: AsyncSession,
     monkeypatch: pytest.MonkeyPatch,
+    patch_session_factory,
 ) -> None:
-    _ = db_session
     calls = {"count": 0}
     logged: list[dict[str, object]] = []