feat: add folder naming service to fix missing years in anime folder names

Runs after NFO refresh during scheduled rescans. Renames folders that
are missing a year (e.g. 'Naruto' → 'Naruto (1999)') using the year
from the database record.

Safety: _build_target_folder() always strips any existing year suffix
first, preventing double/triple year accumulation like
'Naruto (1999) (1999) (1999)'.

Changes:
- New FolderNamingService (folder_naming_service.py) with safe target
  name construction, DB update, and in-memory cache update
- New SchedulerConfig field: folder_naming_after_nfo_scan (default True)
- Integrated as step 3 in scheduler _perform_rescan() after NFO scan
- Runtime UI: existing 'folder-scan-enabled' checkbox in index.html
  now wired to toggle the feature (app.js + scheduler-config.js)
- Setup screen: new checkbox in setup.html Scheduler Settings section
- API: scheduler config endpoint returns all scan toggles
- Tests: 39 unit tests covering static helpers, rename logic, safety
  guard, and integration cases (folder_naming_service.py)
- Docs: testing guide updated with FolderNamingService examples

src/server/api/scheduler.py

@@ -31,6 +31,9 @@ def _build_response(config: SchedulerConfig) -> Dict[str, Any]:
             "schedule_time": config.schedule_time,
             "schedule_days": config.schedule_days,
             "auto_download_after_rescan": config.auto_download_after_rescan,
+            "nfo_scan_after_rescan": config.nfo_scan_after_rescan,
+            "image_scan_after_rescan": config.image_scan_after_rescan,
+            "folder_naming_after_nfo_scan": config.folder_naming_after_nfo_scan,
         },
         "status": {
             "is_running": runtime.get("is_running", False),