Add complete Traditional Chinese UI locale support

Add zh-TW locale resources and wire it through language selection,
persistence, and system-locale detection. Also add static shape typing
for zh-TW to prevent future key drift from zh-CN.

Constraint: Keep changes minimal and localized to i18n + language pickers
Rejected: Partial zh-TW translation only for language section | fails full locale support goal
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep zh-TW key shape locked to zh-CN when adding new translation keys
Tested: npm run -s build (openless-all/app)
Not-tested: Manual runtime walkthrough on all platform shells

Author: H-Chris233

openless-all/app/src/components/SettingsModal.tsx

@@ -333,6 +333,7 @@ function LanguagePicker() {
     >
       <option value={FOLLOW_SYSTEM}>{t('settings.language.followSystem')}</option>
       <option value="zh-CN">{t('settings.language.zh')}</option>
+      <option value="zh-TW">{t('settings.language.zhTW')}</option>
       <option value="en">{t('settings.language.en')}</option>
     </select>
   );

openless-all/app/src/i18n/en.ts

@@ -391,6 +391,7 @@ export const en: typeof zhCN = {
       labelDesc: 'Choose "Follow system" to match the OS language at launch.',
       followSystem: 'Follow system',
       zh: '简体中文',
+      zhTW: '繁體中文',
       en: 'English',
       restartHint: 'Some native menus (system tray, etc.) may require an app restart to fully switch.',
     },

openless-all/app/src/i18n/index.ts

@@ -12,8 +12,9 @@ import i18n from 'i18next';
 import { initReactI18next } from 'react-i18next';
 import { en } from './en';
 import { zhCN } from './zh-CN';
+import { zhTW } from './zh-TW';
 
-export const SUPPORTED_LOCALES = ['zh-CN', 'en'] as const;
+export const SUPPORTED_LOCALES = ['zh-CN', 'zh-TW', 'en'] as const;
 export type SupportedLocale = (typeof SUPPORTED_LOCALES)[number];
 
 export const LOCALE_STORAGE_KEY = 'ol.locale';
@@ -22,21 +23,25 @@ const FOLLOW_SYSTEM_VALUE = 'system';
 function detectSystemLocale(): SupportedLocale {
   if (typeof navigator === 'undefined') return 'zh-CN';
   const nav = (navigator.language || '').toLowerCase();
-  if (nav.startsWith('zh')) return 'zh-CN';
+  if (nav.startsWith('zh')) {
+    if (nav.includes('hant') || nav.includes('tw') || nav.includes('hk') || nav.includes('mo')) return 'zh-TW';
+    return 'zh-CN';
+  }
   return 'en';
 }
 
 function getStoredLocale(): SupportedLocale | null {
   if (typeof window === 'undefined') return null;
   const raw = window.localStorage.getItem(LOCALE_STORAGE_KEY);
-  return raw === 'zh-CN' || raw === 'en' ? raw : null;
+  return raw === 'zh-CN' || raw === 'zh-TW' || raw === 'en' ? raw : null;
 }
 
 const initialLng: SupportedLocale = getStoredLocale() ?? detectSystemLocale();
 
 void i18n.use(initReactI18next).init({
   resources: {
     'zh-CN': { translation: zhCN },
+    'zh-TW': { translation: zhTW },
     en: { translation: en },
   },
   lng: initialLng,

openless-all/app/src/i18n/zh-CN.ts

@@ -389,6 +389,7 @@ export const zhCN = {
       labelDesc: '选择「跟随系统」时按操作系统当前语言显示。',
       followSystem: '跟随系统',
       zh: '简体中文',
+      zhTW: '繁體中文',
       en: 'English',
       restartHint: '部分原生菜单（系统托盘等）可能需要重启 App 才会切换。',
     },