fix: correct tunnel protocol handling for KCP cleanup and diagnosis

- Fix KCP tunnel not reclaimed after deletion: service name was
  hardcoded to {id}_tls but services were created as {id}_kcp,
  causing DeleteService to never find the actual KCP service.
  Now reads tunnel.Protocol from DB and derives correct name.

- Fix KCP diagnosis using TCP ping instead of UDP ping:
  tunnel.Protocol was always hardcoded to 'tls' at creation,
  so isUDPBasedProtocol() never matched kcp tunnels. Now
  stores the actual protocol from entry node configuration.

- Fix addTunnelServiceOnNode to extract service name from
  serviceData instead of hardcoding _tls suffix.

- Fix rollbackTunnelRuntime to accept protocol parameter
  so retry cleanup uses correct service name.

- UpdateTunnelTx now persists protocol on tunnel updates.

go-backend/internal/store/repo/repository_mutations.go

@@ -394,7 +394,7 @@ func (r *Repository) UpdateTunnelOrder(tunnelID int64, inx int, now int64) {
 		Updates(map[string]interface{}{"inx": inx, "updated_time": now}).Error
 }
 
-func (r *Repository) UpdateTunnelTx(tx *gorm.DB, tunnelID int64, name string, typeVal int, flow int64, trafficRatio float64, status int, inIP, ipPreference string, now int64) error {
+func (r *Repository) UpdateTunnelTx(tx *gorm.DB, tunnelID int64, name string, typeVal int, flow int64, trafficRatio float64, status int, inIP, ipPreference string, protocol string, now int64) error {
 	if tx == nil {
 		return errors.New("database unavailable")
 	}
@@ -408,6 +408,7 @@ func (r *Repository) UpdateTunnelTx(tx *gorm.DB, tunnelID int64, name string, ty
 			"status":        status,
 			"in_ip":         nullStringFromInterface(inIP),
 			"ip_preference": ipPreference,
+			"protocol":      protocol,
 			"updated_time":  now,
 		}).Error
 }