fix: handle missing anime directory gracefully on startup

src/server/utils/dependencies.py

@@ -125,6 +125,14 @@ def get_series_app() -> SeriesApp:
                     import tempfile
                     anime_dir = tempfile.gettempdir()
                     settings.anime_directory = anime_dir
+                else:
+                    raise HTTPException(
+                        status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
+                        detail=(
+                            f"Anime directory does not exist: {anime_dir}. "
+                            "Please configure a valid path."
+                        ),
+                    )
 
             _series_app = SeriesApp(anime_dir)
         except Exception as e: