feat(simkl): add comprehensive error handling

SimklFunctions.go:
- Update SimklHelper to return (json.RawMessage, error)
- Add status code validation (200-299 range)
- Update SimklGetUserWatchlist to return (SimklWatchListType, error)
- Update SimklSyncEpisodes to return (SimklAnime, error)
- Update SimklSyncRating to return (SimklAnime, error)
- Update SimklSyncStatus to return (SimklAnime, error)
- Update SimklSearch to return (SimklAnime, error)
- Update SimklSyncRemove to return (bool, error)
- Add proper error wrapping for all failure scenarios

SimklUserFunctions.go:
- Replace log.Fatalf with log.Printf in server error handling (line 119)
- Replace log.Fatal with log.Printf in JSON marshaling (line 141)

All Simkl API calls now properly propagate errors to frontend.

SimklUserFunctions.go

@@ -116,7 +116,7 @@ func (a *App) handleSimklCallback(wg *sync.WaitGroup) {
 	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...")
 	}()
@@ -138,7 +138,8 @@ func getSimklAuthorizationToken(content string) SimklJWT {
 	}
 	jsonData, err := json.Marshal(data)
 	if err != nil {
-		log.Fatal(err)
+		log.Printf("Failed to marshal data: %s\n", err)
+		return SimklJWT{}
 	}
 
 	response, err := http.NewRequest("POST", "https://api.simkl.com/oauth/token", bytes.NewBuffer(jsonData))