chore(kiro): token refresh 실패 로그를 WARN에서 DEBUG로 변경

refresh token invalid_grant 같은 정상적인 토큰 만료 상황에서
WARN 로그가 과도하게 출력되는 문제 수정.

Author: whrho

internal/auth/kiro/refresh_utils.go

@@ -45,7 +45,7 @@ func RefreshWithGracefulDegradation(
 	}
 
 	// Refresh failed - check if we can use the existing token
-	log.Warnf("kiro: token refresh failed: %v", err)
+	log.Debugf("kiro: token refresh failed: %v", err)
 
 	// Check if existing token is still valid (not expired)
 	if existingAccessToken != "" && time.Now().Before(expiresAt) {

internal/auth/kiro/sso_oidc.go

@@ -765,7 +765,7 @@ func (c *SSOOIDCClient) RefreshToken(ctx context.Context, clientID, clientSecret
 	}
 
 	if resp.StatusCode != http.StatusOK {
-		log.Warnf("token refresh failed (status %d): %s", resp.StatusCode, string(respBody))
+		log.Debugf("token refresh failed (status %d): %s", resp.StatusCode, string(respBody))
 		return nil, fmt.Errorf("token refresh failed (status %d): %s", resp.StatusCode, string(respBody))
 	}