Add Google OAuth authentication support

- Add Google OAuth token verification and user lookup/creation
- Add GoogleAuthRequest and GoogleAuthResponse DTOs
- Add GoogleLogin handler in auth_handler.go
- Add google_auth.go service for token verification
- Add FindByGoogleID repository method for user lookup
- Add GoogleID field to User model
- Add Google OAuth configuration (client ID, enabled flag)
- Add i18n translations for Google auth error messages
- Add Google verification email template support

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

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

internal/i18n/translations/zh.json

@@ -21,6 +21,9 @@
   "error.apple_signin_not_configured": "未配置 Apple 登录",
   "error.apple_signin_failed": "Apple 登录失败",
   "error.invalid_apple_token": "Apple 身份令牌无效",
+  "error.google_signin_not_configured": "未配置 Google 登录",
+  "error.google_signin_failed": "Google 登录失败",
+  "error.invalid_google_token": "Google 身份令牌无效",
 
   "error.invalid_task_id": "任务 ID 无效",
   "error.invalid_residence_id": "房产 ID 无效",