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/database/database.go

@@ -124,6 +124,7 @@ func Migrate() error {
 		&models.ConfirmationCode{},
 		&models.PasswordResetCode{},
 		&models.AppleSocialAuth{},
+		&models.GoogleSocialAuth{},
 
 		// Admin users (separate from app users)
 		&models.AdminUser{},