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/configs/config.yaml

@@ -43,6 +43,10 @@ rabbitmq:
   generation_dlq: generation.task.run.dlq
   generation_dlq_routing_key: generation.task.run.dlq
   generation_event_exchange: generation.event
+  desktop_task_event_exchange: desktop.task.event
+  desktop_dispatch_exchange: desktop.task.dispatch
+  desktop_dispatch_publish_prefix: publish
+  desktop_dispatch_monitor_prefix: monitor
   template_assist_exchange: template.assist
   template_assist_routing_key: template.assist.run
   template_assist_queue: template.assist.run