Add comprehensive test coverage for Tasks 1.1–1.5 and 2.1:
- test_scheduler_config_model.py: folder_scan_enabled defaults, explicit
values, backward compatibility with old configs, serialization roundtrip
- test_folder_scan_service.py (new): prerequisites, NFO repair integration,
folder rename integration, poster check/download, semaphore values,
NFO thumb URL extraction, full end-to-end scan flow
- test_scheduler_service.py: scheduler _perform_rescan integration with
folder_scan_enabled (called when enabled, skipped when disabled, error
handling and broadcasting), folder_scan_enabled in get_status output
- test_nfo_repair_startup.py: verify perform_nfo_repair_scan is NOT called
during FastAPI lifespan startup and IS called from FolderScanService
All 90 tests pass.