Refactor localization system and migrate to Fyne's built-in support

Replaced the `i18n` and `toml` dependencies with Fyne's built-in language system for localization management. Updated the `Localizer` implementation to handle translations using JSON files and embed functionality. Simplified language selection and persisted settings via Fyne's preferences API.

handler/main.go

@@ -1,42 +1,32 @@
 package handler
 
 import (
-	"fyne.io/fyne/v2/lang"
 	"git.kor-elf.net/kor-elf/gui-for-ffmpeg/kernel"
-	"git.kor-elf.net/kor-elf/gui-for-ffmpeg/localizer"
 )
 
 type MainHandler struct {
-	app                 kernel.AppContract
-	convertorHandler    ConvertorHandlerContract
-	menuHandler         MenuHandlerContract
-	localizerRepository localizer.RepositoryContract
+	app              kernel.AppContract
+	convertorHandler ConvertorHandlerContract
+	menuHandler      MenuHandlerContract
 }
 
 func NewMainHandler(
 	app kernel.AppContract,
 	convertorHandler ConvertorHandlerContract,
 	menuHandler MenuHandlerContract,
-	localizerRepository localizer.RepositoryContract,
 ) *MainHandler {
 	return &MainHandler{
-		app:                 app,
-		convertorHandler:    convertorHandler,
-		menuHandler:         menuHandler,
-		localizerRepository: localizerRepository,
+		app:              app,
+		convertorHandler: convertorHandler,
+		menuHandler:      menuHandler,
 	}
 }
 
 func (h MainHandler) Start() {
-	language := h.localizerRepository.GetCode()
-	if len(language) == 0 {
-		err := h.app.GetLocalizerService().SetCurrentLanguageByCode(lang.SystemLocale().LanguageString())
-		if err != nil {
-			h.menuHandler.LanguageSelection()
-			return
-		}
+	if h.app.GetLocalizerService().IsStartWithLanguageSelection() {
+		h.menuHandler.LanguageSelection()
+		return
 	}
-	_ = h.app.GetLocalizerService().SetCurrentLanguageByCode(language)
 
 	h.convertorHandler.MainConvertor()
 }