refactor: Simplify platform-specific icon handling in AppCustomizationPage and ProfilePage

- Replaced direct platform checks with a utility method `UiUtils.platformIcon` for better readability and maintainability.
- Updated localization strings for app customization to enhance clarity and consistency across multiple languages.
- Adjusted icon colors in the UI to ensure proper theming and visual consistency.

lib/l10n/app_zh.arb

@@ -233,7 +233,7 @@
   "deleteFolderTitle": "删除文件夹",
   "deleteFolderMessage": "此文件夹及其分配引用将被删除。",
   "failedToDeleteFolder": "无法删除文件夹",
-  "aboutApp": "关于应用",
+  "aboutApp": "关于",
   "aboutAppSubtitle": "Conduit 信息和链接",
   "web": "网页",
   "imageGen": "图像生成",
@@ -303,8 +303,8 @@
     "description": "显示助手在回复前思考了多长时间。",
     "placeholders": {"duration": {"type": "String", "example": "3s"}}
   },
-  "appCustomization": "应用自定义",
-  "appCustomizationSubtitle": "个性化名称和 UI 显示",
+  "appCustomization": "自定义",
+  "appCustomizationSubtitle": "主题、语言、语音和 quickpills",
   "quickActionsDescription": "选择最多两个快捷方式以固定在撰写器附近",
   "chatSettings": "对话",
   "sendOnEnter": "回车发送",