feat: add Japanese (ja-JP) language support (#1537)

* feat: add Japanese (ja-JP) language support

- Add comprehensive Japanese translation file (ja-JP.ts)
- Update i18n configuration to include Japanese locale
- Add Japanese language option to login and register page dropdowns
- Implement Japanese language detection and switching logic
- Maintain fallback to en-US for missing translations in flexible components

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

* perf: ui for ja-JP

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
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/index.ts

@@ -6,6 +6,7 @@ import LanguageDetector from 'i18next-browser-languagedetector';
 
 import enUS from './locales/en-US';
 import zhHans from './locales/zh-Hans';
+import jaJP from './locales/ja-JP';
 
 i18n
   .use(LanguageDetector)
@@ -18,6 +19,9 @@ i18n
       'zh-Hans': {
         translation: zhHans,
       },
+      'ja-JP': {
+        translation: jaJP,
+      },
     },
     fallbackLng: 'zh-Hans',
     debug: process.env.NODE_ENV === 'development',