feat(admin): 添加 LinuxDO OAuth 回调地址快速设置按钮

- 在设置页面添加"使用当前站点生成并复制"按钮
- 自动填充回调地址并复制到剪贴板
- 添加中英文国际化支持

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/i18n/locales/en.ts

@@ -1782,7 +1782,9 @@ export default {
         redirectUrl: 'Redirect URL',
         redirectUrlPlaceholder: 'https://your-domain.com/api/v1/auth/oauth/linuxdo/callback',
         redirectUrlHint:
-          'Must match the redirect URL configured in Connect.Linux.Do (must be an absolute http(s) URL)'
+          'Must match the redirect URL configured in Connect.Linux.Do (must be an absolute http(s) URL)',
+        quickSetCopy: 'Generate & Copy (current site)',
+        redirectUrlSetAndCopied: 'Redirect URL generated and copied to clipboard'
       },
       defaults: {
         title: 'Default User Settings',

frontend/src/i18n/locales/zh.ts

@@ -1926,7 +1926,9 @@ export default {
         clientSecretConfiguredHint: '密钥已配置，留空以保留当前值。',
         redirectUrl: '回调地址（Redirect URL）',
         redirectUrlPlaceholder: 'https://your-domain.com/api/v1/auth/oauth/linuxdo/callback',
-        redirectUrlHint: '需与 Connect.Linux.Do 中配置的回调地址一致（必须是 http(s) 完整 URL）'
+        redirectUrlHint: '需与 Connect.Linux.Do 中配置的回调地址一致（必须是 http(s) 完整 URL）',
+        quickSetCopy: '使用当前站点生成并复制',
+        redirectUrlSetAndCopied: '已使用当前站点生成回调地址并复制到剪贴板'
       },
       defaults: {
         title: '用户默认设置',