feat: internationalize API error responses by locale

Add shared error codes with zh/en/ms messages, coded app exceptions,
and locale-aware global filter. Frontends send X-Locale so error text
matches the active UI language.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/player/src/api/index.ts

@@ -5,6 +5,10 @@ const api = axios.create({ baseURL: '/api' });
 api.interceptors.request.use((config) => {
   const token = localStorage.getItem('token');
   if (token) config.headers.Authorization = `Bearer ${token}`;
+
+  const locale = localStorage.getItem('locale') || 'zh-CN';
+  config.headers['X-Locale'] = locale;
+
   return config;
 });