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.

theme/theme.go

@@ -55,10 +55,7 @@ func (t theme) List() map[string]ThemeInfoContract {
 }
 
 func (t theme) SetCurrentTheme(themeInfo ThemeInfoContract) error {
-	_, err := t.repository.Save(themeInfo.GetName())
-	if err != nil {
-		return err
-	}
+	_ = t.repository.Save(themeInfo.GetName())
 
 	if themeInfo.GetName() == "default" {
 		t.app.GetAppFyne().Settings().SetTheme(fyneTheme.DefaultTheme())