feat(nodes): add Dev channel option to node panel updates

The node update confirm dialog now offers a 'Dev channel (latest commit)' choice. The dev flag threads master -> nodes/updatePanel -> UpdatePanels -> remote.UpdatePanel -> the node's updatePanel endpoint, which calls StartUpdateChannel(dev) to install the rolling dev-latest build. With no dev flag the node keeps following its own channel setting.

internal/web/service/node.go

@@ -637,7 +637,7 @@ type NodeUpdateResult struct {
 // UpdatePanels triggers the official self-updater on each given node. Only
 // enabled, online nodes are eligible — an offline node can't be reached, so it
 // is reported as skipped rather than silently dropped.
-func (s *NodeService) UpdatePanels(ids []int) ([]NodeUpdateResult, error) {
+func (s *NodeService) UpdatePanels(ids []int, dev bool) ([]NodeUpdateResult, error) {
 	mgr := runtime.GetManager()
 	if mgr == nil {
 		return nil, fmt.Errorf("runtime manager unavailable")
@@ -662,7 +662,7 @@ func (s *NodeService) UpdatePanels(ids []int) ([]NodeUpdateResult, error) {
 				break
 			}
 			ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
-			updErr := remote.UpdatePanel(ctx)
+			updErr := remote.UpdatePanel(ctx, dev)
 			cancel()
 			if updErr != nil {
 				res.Error = updErr.Error()

internal/web/service/panel/panel.go

@@ -122,8 +122,19 @@ func getDevUpdateInfo() (*PanelUpdateInfo, error) {
 	}, nil
 }
 
-// StartUpdate starts the official updater outside of the current web request.
+// StartUpdate starts the official updater using this panel's own channel setting.
 func (s *PanelService) StartUpdate() error {
+	return s.startUpdate(devChannelActive())
+}
+
+// StartUpdateChannel runs the updater against an explicitly chosen channel,
+// overriding the local dev-channel setting. Used by the master node updater so
+// a node can be moved to the dev channel from the central panel.
+func (s *PanelService) StartUpdateChannel(dev bool) error {
+	return s.startUpdate(dev)
+}
+
+func (s *PanelService) startUpdate(useDev bool) error {
 	if runtime.GOOS != "linux" {
 		return fmt.Errorf("panel web update is supported only on Linux installations")
 	}
@@ -140,7 +151,7 @@ func (s *PanelService) StartUpdate() error {
 
 	mainFolder, serviceFolder := resolveUpdateFolders()
 	updateTag := ""
-	if devChannelActive() {
+	if useDev {
 		updateTag = devReleaseTag
 	}
 	updateScript := fmt.Sprintf("set -e; trap 'rm -f %s' EXIT; %s %s", shellQuote(scriptPath), shellQuote(bash), shellQuote(scriptPath))