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_publication_pdf_resolution_pipeline.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 from datetime import UTC, datetime
 from types import SimpleNamespace
+from typing import Any
 
 import pytest
 
@@ -11,7 +12,7 @@ from app.services.publications import pdf_resolution_pipeline as pipeline
 from app.services.unpaywall.application import OaResolutionOutcome
 
 
-def _row(*, display_identifier: DisplayIdentifier | None = None) -> SimpleNamespace:
+def _row(*, display_identifier: DisplayIdentifier | None = None) -> Any:
     return SimpleNamespace(
         publication_id=1,
         scholar_profile_id=1,