feat(gateway): 创建/编辑网关后立即异步探活健康状态

- POST/PUT /api/gateways 成功后后台立即探活一次 /healthz 并覆盖落库，不阻塞请求
- probeAndRecordGateway 抽出单网关探活+落库复用；探活超时改为 var 供测试注入
- 网关页保存成功后延迟 2.5s 刷新一次，尽快展示最新健康状态
- 测试：立即探活、慢网关不阻塞、不可达落 unhealthy

internal/controlplane/api/environments.go

@@ -26,6 +26,7 @@ type HubStore interface {
 	ListGateways(ctx context.Context) ([]hub.Gateway, error)
 	GetGateway(ctx context.Context, name string) (hub.Gateway, error)
 	DeleteGateway(ctx context.Context, name string) error
+	RecordGatewayCheck(ctx context.Context, name, status, reason string) (hub.Gateway, error)
 	ListEnvs(ctx context.Context) ([]hub.Env, error)
 	GetEnv(ctx context.Context, alias string) (hub.Env, error)
 	CreateNetworkExit(ctx context.Context, exit hub.NetworkExit) (hub.NetworkExit, error)
@@ -488,6 +489,7 @@ func registerHubWithNetwork(app *fiber.App, store HubStore, probe NetworkExitPro
 		if err != nil {
 			return hubError(c, err)
 		}
+		probeGatewayAsync(c.Context(), store, gateway)
 		return c.Status(fiber.StatusCreated).JSON(gateway)
 	})
 	app.Put("/api/gateways/:name", func(c fiber.Ctx) error {
@@ -503,6 +505,7 @@ func registerHubWithNetwork(app *fiber.App, store HubStore, probe NetworkExitPro
 		if err != nil {
 			return hubError(c, err)
 		}
+		probeGatewayAsync(c.Context(), store, gateway)
 		return c.JSON(gateway)
 	})
 	app.Delete("/api/gateways/:name", func(c fiber.Ctx) error {