chore(i18n): 补充界面缩放设置的中英文文案并清理多余键

- en-US / zh-CN 新增 app.appearance-settings.ui-scale.title 与
  .description；
- 移除未使用的 ui-scale.custom / ui-scale.percent 文案键。

apps/app-frontend/src/components/ui/settings/AppearanceSettings.vue

@@ -219,14 +219,6 @@ const messages = defineMessages({
 		defaultMessage:
 			'Scale the whole launcher interface. A smaller scale fits more content, which helps when embedded pages are cut off.',
 	},
-	uiScaleCustom: {
-		id: 'app.appearance-settings.ui-scale.custom',
-		defaultMessage: 'Custom',
-	},
-	uiScalePercent: {
-		id: 'app.appearance-settings.ui-scale.percent',
-		defaultMessage: '{value}%',
-	},
 	pageTransitionsTitle: {
 		id: 'app.appearance-settings.page-transitions.title',
 		defaultMessage: 'Page transition animations',