Add directory selection for saving converted files

Introduce logic and UI for selecting and persisting a directory to save converted files. Extend existing components with directory selection buttons, message updates, and storage preferences.

internal/application/setting/setting.go

@@ -10,10 +10,16 @@ type SettingContract interface {
 	GetLanguages() []Lang
 	GetCurrentLangOrDefaultLang() (currentLang Lang, isDefault bool)
 	SetLang(language Lang) error
+
+	GetDirectoryForSaving() string
+	SetDirectoryForSaving(path string)
+
 	GetFFmpegPath() string
 	SetFFmpegPath(path string)
+
 	GetFFprobePath() string
 	SetFFprobePath(path string)
+
 	GetFFplayPath() string
 	SetFFplayPath(path string)
 }
@@ -63,3 +69,11 @@ func (s *setting) SetLang(language Lang) error {
 	s.fyneApp.Preferences().SetString("language", language.Code)
 	return nil
 }
+
+func (s *setting) GetDirectoryForSaving() string {
+	return s.fyneApp.Preferences().String("directoryForSaving")
+}
+
+func (s *setting) SetDirectoryForSaving(path string) {
+	s.fyneApp.Preferences().SetString("directoryForSaving", path)
+}