Add main settings view and theme management functionality

Introduce a new `MainSettings` view for managing application settings, including language and theme selection. Implement theme management methods in the `setting` package to handle theme initialization, retrieval, and updates.

internal/gui/view/mainSettings.go

@@ -0,0 +1,92 @@
+package view
+
+import (
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/canvas"
+	"fyne.io/fyne/v2/lang"
+	"fyne.io/fyne/v2/widget"
+	"git.kor-elf.net/kor-elf/gui-for-ffmpeg/internal/application/setting"
+	"image/color"
+)
+
+type MainSettingForm struct {
+	Language  setting.Lang
+	ThemeInfo setting.ThemeInfoContract
+}
+
+func MainSettings(
+	currentLang setting.Lang,
+	langList []setting.Lang,
+
+	themeInfo setting.ThemeInfoContract,
+	themeList map[string]setting.ThemeInfoContract,
+
+	save func(form *MainSettingForm) error,
+	cancel func(),
+) fyne.CanvasObject {
+
+	errorMessage := canvas.NewText("", color.RGBA{R: 255, G: 0, B: 0, A: 255})
+	errorMessage.TextSize = 16
+	errorMessage.TextStyle = fyne.TextStyle{Bold: true}
+
+	viewSettingForm := &MainSettingForm{
+		Language:  currentLang,
+		ThemeInfo: themeInfo,
+	}
+
+	var languageItems []string
+	langByTitle := map[string]setting.Lang{}
+	for _, language := range langList {
+		languageItems = append(languageItems, language.Title)
+		langByTitle[language.Title] = language
+	}
+	selectLanguage := widget.NewSelect(languageItems, func(s string) {
+		if lang, ok := langByTitle[s]; ok {
+			viewSettingForm.Language = lang
+		}
+	})
+	selectLanguage.Selected = currentLang.Title
+
+	var themeItems []string
+	themeByTitle := map[string]setting.ThemeInfoContract{}
+	for _, themeInfo := range themeList {
+		themeItems = append(themeItems, themeInfo.GetTitle())
+		themeByTitle[themeInfo.GetTitle()] = themeInfo
+	}
+	selectTheme := widget.NewSelect(themeItems, func(s string) {
+		if themeInfo, ok := themeByTitle[s]; ok {
+			viewSettingForm.ThemeInfo = themeInfo
+		}
+	})
+	selectTheme.Selected = themeInfo.GetTitle()
+
+	form := &widget.Form{
+		Items: []*widget.FormItem{
+			{
+				Text:   lang.L("menuSettingsLanguage"),
+				Widget: selectLanguage,
+			},
+			{
+				Text:   lang.L("menuSettingsTheme"),
+				Widget: selectTheme,
+			},
+			{
+				Widget: errorMessage,
+			},
+		},
+		SubmitText: lang.L("save"),
+		OnSubmit: func() {
+			err := save(viewSettingForm)
+			if err != nil {
+				errorMessage.Text = err.Error()
+			}
+		},
+	}
+	if cancel != nil {
+		form.OnCancel = cancel
+		form.CancelText = lang.L("cancel")
+	}
+
+	messageHead := lang.L("settings")
+	return widget.NewCard(messageHead, "", form)
+}