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_scholars_create_hydration.py

@@ -1,4 +1,5 @@
 from types import SimpleNamespace
+from typing import Any, cast
 
 import pytest
 
@@ -42,9 +43,9 @@ async def test_create_hydration_skips_when_global_throttle_active(
     )
 
     result = await scholar_helpers.hydrate_scholar_metadata_if_needed(
-        db_session=None,
+        db_session=cast(Any, None),
         profile=profile,
-        source=object(),
+        source=cast(Any, object()),
         user_id=7,
     )
 
@@ -77,9 +78,9 @@ async def test_create_hydration_runs_when_throttle_is_clear(
     )
 
     result = await scholar_helpers.hydrate_scholar_metadata_if_needed(
-        db_session=None,
+        db_session=cast(Any, None),
         profile=profile,
-        source=object(),
+        source=cast(Any, object()),
         user_id=8,
     )
 
@@ -109,7 +110,7 @@ async def test_initial_scrape_job_enqueued_on_create(
     )
 
     queued = await scholar_helpers.enqueue_initial_scrape_job_for_scholar(
-        session,
+        cast(Any, session),
         profile=profile,
         user_id=9,
     )
@@ -134,7 +135,7 @@ async def test_initial_scrape_job_not_enqueued_when_disabled(
     )
 
     queued = await scholar_helpers.enqueue_initial_scrape_job_for_scholar(
-        session,
+        cast(Any, session),
         profile=profile,
         user_id=11,
     )