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.

theme/theme.go

@@ -4,7 +4,6 @@ import (
 	"fyne.io/fyne/v2"
 	fyneTheme "fyne.io/fyne/v2/theme"
 	"git.kor-elf.net/kor-elf/gui-for-ffmpeg/kernel"
-	"github.com/nicksnyder/go-i18n/v2/i18n"
 	"image/color"
 )
 
@@ -92,25 +91,19 @@ func (inf themeInfo) GetVariant() fyne.ThemeVariant {
 
 func getThemes(localizer kernel.LocalizerContract) map[string]ThemeInfoContract {
 	themesNameDefault := &themeInfo{
-		name: "default",
-		title: localizer.GetMessage(&i18n.LocalizeConfig{
-			MessageID: "themesNameDefault",
-		}),
+		name:  "default",
+		title: localizer.GetMessage("themesNameDefault"),
 	}
 
 	themesNameLight := &themeInfo{
-		name: "light",
-		title: localizer.GetMessage(&i18n.LocalizeConfig{
-			MessageID: "themesNameLight",
-		}),
+		name:    "light",
+		title:   localizer.GetMessage("themesNameLight"),
 		variant: fyneTheme.VariantLight,
 	}
 
 	themesNameDark := &themeInfo{
-		name: "dark",
-		title: localizer.GetMessage(&i18n.LocalizeConfig{
-			MessageID: "themesNameDark",
-		}),
+		name:    "dark",
+		title:   localizer.GetMessage("themesNameDark"),
 		variant: fyneTheme.VariantDark,
 	}