refactor: fix naming, remove duplicate code from decomposition

- Rename _int_or_default → int_or_default (public API, was using private convention)
- Extract shared pdf_queue utilities (utcnow, event_row, queued_job, status constants) to pdf_queue_common.py to avoid circular imports
- Consolidate _effective_request_delay_seconds into queue_runner.py with explicit floor parameter
- Update tests to match new function locations and names

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

tests/unit/test_request_delay_policy.py

@@ -4,6 +4,7 @@ from datetime import UTC, datetime
 
 from app.services.ingestion import scheduler as scheduler_module
 from app.services.ingestion.application import ScholarIngestionService
+from app.services.ingestion.queue_runner import effective_request_delay_seconds
 from app.settings import settings
 
 
@@ -25,9 +26,9 @@ def test_ingestion_effective_request_delay_respects_policy_minimum() -> None:
 def test_scheduler_effective_request_delay_respects_policy_minimum() -> None:
     previous = _set_policy_minimum(9)
     try:
-        assert scheduler_module._effective_request_delay_seconds(None) == 9
-        assert scheduler_module._effective_request_delay_seconds(6) == 9
-        assert scheduler_module._effective_request_delay_seconds(11) == 11
+        assert effective_request_delay_seconds(None, floor=9) == 9
+        assert effective_request_delay_seconds(6, floor=9) == 9
+        assert effective_request_delay_seconds(11, floor=9) == 11
     finally:
         object.__setattr__(settings, "ingestion_min_request_delay_seconds", previous)