feat: 将"关于"从系统托盘原生对话框迁移到前端页面

移除系统托盘右键菜单中的"关于"选项及各平台原生对话框实现，
在前端新增 /about 路由和关于页面展示品牌信息，侧边栏增加关于导航入口

backend/cmd/desktop/dialog_linux.go

@@ -65,21 +65,3 @@ func showError(title, message string) {
 		dialogLogger().Error("无法显示错误对话框")
 	}
 }
-
-func showAbout() {
-	switch dialogTool {
-	case toolZenity:
-		exec.Command("zenity", "--info",
-			fmt.Sprintf("--title=%s", appAboutTitle),
-			fmt.Sprintf("--text=%s", aboutMessage())).Run()
-	case toolKdialog:
-		exec.Command("kdialog", "--msgbox", aboutMessage(), "--title", appAboutTitle).Run()
-	case toolNotifySend:
-		exec.Command("notify-send", appAboutTitle, aboutMessage()).Run()
-	case toolXmessage:
-		exec.Command("xmessage", "-center",
-			fmt.Sprintf("%s: %s", appAboutTitle, aboutMessage())).Run()
-	default:
-		dialogLogger().Info(appAboutTitle)
-	}
-}