feat: 优化 OAuth 账号导入流程

backend/internal/service/token_refresher.go

@@ -2,6 +2,7 @@ package service
 
 import (
 	"context"
+	"strings"
 	"time"
 )
 
@@ -95,6 +96,9 @@ func (r *OpenAITokenRefresher) CanRefresh(account *Account) bool {
 // NeedsRefresh 检查token是否需要刷新
 // expires_at 缺失且处于限流状态时需要刷新，防止限流期间 token 静默过期
 func (r *OpenAITokenRefresher) NeedsRefresh(account *Account, refreshWindow time.Duration) bool {
+	if strings.TrimSpace(account.GetOpenAIRefreshToken()) == "" {
+		return false
+	}
 	expiresAt := account.GetCredentialAsTime("expires_at")
 	if expiresAt == nil {
 		return account.IsRateLimited()