Remove bbolt database dependency

Replaced bbolt-based database handling with Fyne built-in preferences for storing application settings. Deleted migration logic, database initialization, and error handling related to bbolt, simplifying the codebase and reducing external dependencies.

handler/main.go

@@ -28,9 +28,9 @@ func NewMainHandler(
 }
 
 func (h MainHandler) Start() {
-	language, err := h.localizerRepository.GetCode()
-	if err != nil {
-		err = h.app.GetLocalizerService().SetCurrentLanguageByCode(lang.SystemLocale().LanguageString())
+	language := h.localizerRepository.GetCode()
+	if len(language) == 0 {
+		err := h.app.GetLocalizerService().SetCurrentLanguageByCode(lang.SystemLocale().LanguageString())
 		if err != nil {
 			h.menuHandler.LanguageSelection()
 			return