refactor: move NFO repair from initialization_service to folder_scan_service

Moves perform_nfo_repair_scan and its helpers (_repair_one_series,
_NFO_REPAIR_SEMAPHORE) into folder_scan_service.py so NFO repair runs
during the scheduled folder scan instead of on startup.

- Removes NFO repair code from initialization_service.py
- Updates all test imports and patch targets
- Updates docs/NFO_GUIDE.md and docs/CHANGELOG.md references

All 174 related tests pass.

tests/unit/test_folder_scan_service.py

@@ -20,6 +20,7 @@ from src.server.services.folder_scan_service import (
     _TMDB_SEMAPHORE,
     FolderScanService,
     FolderScanServiceError,
+    perform_nfo_repair_scan,
 )
 
 # ---------------------------------------------------------------------------