feat: 添加账号时支持同步上游模型

新增 POST /admin/accounts/models/sync-upstream-preview 端点，
允许在创建账号流程中直接使用凭证同步上游支持的模型，
无需先保存账号获取 ID。

- 后端: 新增 SyncUpstreamModelsPreview handler
- 前端: 新增 syncUpstreamModelsPreview API 函数
- 前端: ModelWhitelistSelector 支持 syncCredentials prop
- 前端: CreateAccountModal 传递凭证给 ModelWhitelistSelector

backend/internal/handler/admin/account_handler.go

@@ -2131,6 +2131,56 @@ func (h *AccountHandler) SyncUpstreamModels(c *gin.Context) {
 	response.Success(c, gin.H{"models": models})
 }
 
+// SyncUpstreamModelsPreview handles syncing live supported models using provided credentials (no account ID needed).
+// POST /api/v1/admin/accounts/models/sync-upstream-preview
+func (h *AccountHandler) SyncUpstreamModelsPreview(c *gin.Context) {
+	var req struct {
+		Platform string `json:"platform" binding:"required"`
+		Type     string `json:"type" binding:"required"`
+		BaseURL  string `json:"base_url"`
+		APIKey   string `json:"api_key" binding:"required"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, "Invalid request: "+err.Error())
+		return
+	}
+
+	tempAccount := &service.Account{
+		Platform: req.Platform,
+		Type:     req.Type,
+		Credentials: map[string]any{
+			"api_key":  req.APIKey,
+			"base_url": req.BaseURL,
+		},
+	}
+
+	if h.accountTestService == nil {
+		response.InternalError(c, "Account test service is not configured")
+		return
+	}
+
+	models, err := h.accountTestService.FetchUpstreamSupportedModels(c.Request.Context(), tempAccount)
+	if err != nil {
+		var syncErr *service.UpstreamModelSyncError
+		if errors.As(err, &syncErr) {
+			switch syncErr.Kind {
+			case service.UpstreamModelSyncErrorConfiguration, service.UpstreamModelSyncErrorUnsupported:
+				response.BadRequest(c, syncErr.SafeMessage())
+			default:
+				slog.Warn("sync_upstream_models_preview_failed", "platform", req.Platform, "kind", syncErr.Kind)
+				response.Error(c, http.StatusBadGateway, syncErr.SafeMessage())
+			}
+			return
+		}
+
+		slog.Warn("sync_upstream_models_preview_failed", "platform", req.Platform)
+		response.Error(c, http.StatusBadGateway, "Failed to sync upstream models from upstream")
+		return
+	}
+
+	response.Success(c, gin.H{"models": models})
+}
+
 // SetPrivacy handles setting privacy for a single OpenAI/Antigravity OAuth account
 // POST /api/v1/admin/accounts/:id/set-privacy
 func (h *AccountHandler) SetPrivacy(c *gin.Context) {

backend/internal/server/routes/admin.go

@@ -302,6 +302,7 @@ func registerAccountRoutes(admin *gin.RouterGroup, h *handler.Handlers) {
 		accounts.GET("/:id/temp-unschedulable", h.Admin.Account.GetTempUnschedulable)
 		accounts.DELETE("/:id/temp-unschedulable", h.Admin.Account.ClearTempUnschedulable)
 		accounts.POST("/:id/schedulable", h.Admin.Account.SetSchedulable)
+		accounts.POST("/models/sync-upstream-preview", h.Admin.Account.SyncUpstreamModelsPreview)
 		accounts.GET("/:id/models", h.Admin.Account.GetAvailableModels)
 		accounts.POST("/:id/models/sync-upstream", h.Admin.Account.SyncUpstreamModels)
 		accounts.POST("/batch", h.Admin.Account.BatchCreate)