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/test_scholar_search_safety.py

@@ -23,6 +23,12 @@ class StubScholarSource:
         index = min(self.calls - 1, len(self._fetch_results) - 1)
         return self._fetch_results[index]
 
+    async def fetch_profile_html(self, scholar_id: str) -> FetchResult:
+        raise NotImplementedError
+
+    async def fetch_profile_page_html(self, scholar_id: str, *, cstart: int, pagesize: int) -> FetchResult:
+        raise NotImplementedError
+
 
 def _ok_author_search_fetch() -> FetchResult:
     body = (