feat(desktop): push publish tasks via AMQP topic dispatch WebSocket

Introduce a desktop.task.dispatch topic exchange with per-client routing
keys. Tenant-api publishes a task_available frame keyed by target client
ID when a publish job is created; every instance binds its own transient
queue and forwards to the matching WebSocket (/api/desktop/dispatch) it
owns. Desktop-client now prefers this push channel and only falls back
to HTTP /lease polling when the socket is down. Also drop admin-web
monitoring-plugin remnants and scope the publish modal account list to
publish platforms.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/transport/router.go

@@ -29,6 +29,7 @@ func RegisterRoutes(app *bootstrap.App) {
 	desktopAccountHandler := NewDesktopAccountHandler(app)
 	desktopTaskHandler := NewDesktopTaskHandler(app)
 	desktopEventsHandler := NewDesktopEventsHandler(app)
+	desktopDispatchHandler := NewDesktopDispatchHandler(app)
 	desktopContentHandler := NewDesktopContentHandler(app)
 	publishJobHandler := NewPublishJobHandler(app)
 	protected.POST("/desktop/clients/register", desktopClientHandler.Register)
@@ -40,6 +41,7 @@ func RegisterRoutes(app *bootstrap.App) {
 	desktopAuth.POST("/clients/offline", desktopClientHandler.Offline)
 	desktopAuth.POST("/clients/revoke", desktopClientHandler.Revoke)
 	desktopAuth.GET("/events", desktopEventsHandler.Stream)
+	desktopAuth.GET("/dispatch", desktopDispatchHandler.Dispatch)
 	desktopAuth.GET("/accounts", desktopAccountHandler.List)
 	desktopAuth.GET("/content/articles/:id", desktopContentHandler.Article)
 	desktopAuth.GET("/publish-tasks", desktopTaskHandler.ListPublish)