feat: add i18n support for initialization page and fix plugin loading text

- Add language selector to register/initialization page with Chinese and English options
- Add register section translations to both zh-Hans.ts and en-US.ts
- Replace hardcoded Chinese texts in register page with i18n translation calls
- Fix hardcoded '加载中...' text in plugin configuration dialog to use t('plugins.loading')
- Follow existing login page pattern for language selector implementation
- Maintain consistent UI/UX design with proper language switching functionality

Co-Authored-By: Junyan Qin <Chin>, 秦骏言 in Chinese, you can call me my english name Rock Chin. <rockchinq@gmail.com>

web/src/i18n/locales/en-US.ts

@@ -203,6 +203,15 @@ const enUS = {
       'Are you sure you want to delete this pipeline? Bots bound to this pipeline will not work.',
     defaultPipelineCannotDelete: 'Default pipeline cannot be deleted',
   },
+  register: {
+    title: 'Initialize LangBot 👋',
+    description: 'This is your first time starting LangBot',
+    adminAccountNote:
+      'The email and password you fill in will be used as the initial administrator account',
+    register: 'Register',
+    initSuccess: 'Initialization successful, please login',
+    initFailed: 'Initialization failed: ',
+  },
 };
 
 export default enUS;