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/models/config.py

@@ -52,6 +52,12 @@ class SchedulerConfig(BaseModel):
         description="Download series images (poster.jpg, fanart.jpg, logo.png) "
                     "from TMDB after a scheduled rescan completes.",
     )
+    folder_naming_after_nfo_scan: bool = Field(
+        default=True,
+        description="Fix missing years in folder names after NFO refresh. "
+                    "Renames folders (e.g. 'Naruto' -> 'Naruto (1999)') using "
+                    "the year from the database record.",
+    )
     # Legacy alias fields — read via Pydantic alias
     auto_download: Optional[bool] = Field(default=None, alias="auto_download")