Fix Code Duplication 4: Create media utilities module

- Created src/server/utils/media.py with reusable media file functions
- Functions: check_media_files(), get_media_file_paths(), has_all_images(), count_video_files(), has_video_files()
- Defined standard filename constants: POSTER_FILENAME, LOGO_FILENAME, FANART_FILENAME, NFO_FILENAME
- Defined VIDEO_EXTENSIONS set for media player compatibility
- Refactored src/server/api/nfo.py (7 locations) to use utility functions
- Refactored src/server/services/background_loader_service.py to use utility
- Functions accept both str and Path for compatibility
- Marked Code Duplications 1, 3, 4 as RESOLVED in instructions.md
- Updated Further Considerations as RESOLVED (addressed in Issues 7, 9, 10)

src/server/services/background_loader_service.py

@@ -234,6 +234,7 @@ class BackgroundLoaderService:
         
         # Check database for series info
         from src.server.database.service import AnimeSeriesService
+        from src.server.utils.media import check_media_files
         
         series_db = await AnimeSeriesService.get_by_key(db, key)
         if not series_db:
@@ -244,19 +245,25 @@ class BackgroundLoaderService:
         # Check episodes
         missing["episodes"] = not series_db.episodes_loaded
         
+        # Check files using utility function
+        folder_path = Path(anime_directory) / folder
+        media_status = check_media_files(
+            folder_path,
+            check_poster=True,
+            check_logo=True,
+            check_fanart=True,
+            check_nfo=True
+        )
+        
         # Check NFO file
-        nfo_path = Path(anime_directory) / folder / "tvshow.nfo"
-        missing["nfo"] = not nfo_path.exists() or not series_db.has_nfo
+        missing["nfo"] = not media_status.get("nfo", False) or not series_db.has_nfo
         
         # Check logo
-        logo_path = Path(anime_directory) / folder / "logo.png"
-        missing["logo"] = not logo_path.exists() or not series_db.logo_loaded
+        missing["logo"] = not media_status.get("logo", False) or not series_db.logo_loaded
         
         # Check images (poster and fanart)
-        poster_path = Path(anime_directory) / folder / "poster.jpg"
-        fanart_path = Path(anime_directory) / folder / "fanart.jpg"
         missing["images"] = (
-            not (poster_path.exists() and fanart_path.exists()) 
+            not (media_status.get("poster", False) and media_status.get("fanart", False))
             or not series_db.images_loaded
         )