feat(mal): add comprehensive error handling

MALFunctions.go:
- Update MALHelper to return (json.RawMessage, string, error)
- Add network error handling and proper request error checking
- Update GetMyAnimeList to return (MALWatchlist, error)
- Update MyAnimeListUpdate to return (MalListStatus, error)
- Update GetMyAnimeListAnime to return (MALAnime, error)
- Update DeleteMyAnimeListEntry to return (bool, error)

MALUserFunctions.go:
- Replace log.Fatalf with log.Printf in server error handling
- Prevent server shutdown on OAuth callback errors

All MAL API calls now properly propagate errors to frontend.

MALUserFunctions.go

@@ -176,7 +176,7 @@ func (a *App) handleMyAnimeListCallback(wg *sync.WaitGroup, verifier *CodeVerifi
 	go func() {
 		defer wg.Done()
 		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
-			log.Fatalf("listen: %s\n", err)
+			log.Printf("Server error: %s\n", err)
 		}
 		fmt.Println("Shutting down...")
 	}()