fix(folder_rename_service): use get_by_folder instead of get_by_key when looking up by folder name

Update_database_paths and duplicate folder cleanup were using get_by_key()
(provider key lookup) instead of get_by_folder() when operating on folder names.
This caused orphaned DB records when removing duplicate folders like 'Hells Paradise'
that mapped to an already-existing 'Hell\'s Paradise (2023)'.

src/server/services/folder_rename_service.py

@@ -403,7 +403,7 @@ async def _update_database_paths(
 
     async with get_db_session() as db:
         # 1. Update AnimeSeries.folder
-        series = await AnimeSeriesService.get_by_key(db, old_folder)
+        series = await AnimeSeriesService.get_by_folder(db, old_folder)
         if series is None:
             # Fallback: try to find by folder name
             all_series = await AnimeSeriesService.get_all(db)
@@ -615,7 +615,7 @@ async def validate_and_rename_series_folders(dry_run: bool = False) -> Dict[str,
 
                 # Delete source DB record (cascades to episodes and download items)
                 async with get_db_session() as db:
-                    source_series = await AnimeSeriesService.get_by_key(db, current_name)
+                    source_series = await AnimeSeriesService.get_by_folder(db, current_name)
                     if source_series is None:
                         # Fallback: find by folder name
                         all_series = await AnimeSeriesService.get_all(db)