feat(broadcasting): add ActionCable adapter + fix model broadcast anti-pattern

- Add Mozo::Broadcaster::ActionCable as drop-in Faye replacement
- Fix model_broadcast.rb: delegate to Mozo directly instead of
  ApplicationController.new (memory-unsafe anti-pattern)
- Add Broadcastable concern for clean model-side broadcasting
- ActionCable config: async adapter, cable.yml, WebSocket endpoint
- MozoChannel with per-entity authorization (user/supplier/employee)
- Connection auth via auth_token (matches existing auth pattern)
- Mount /cable WebSocket in routes
- Add broadcasting-migration.md with Faye→ActionCable guide

config/initializers/model_broadcast.rb

@@ -1,12 +1,31 @@
-#TODO: this is really ugly, can cause memory leaks and much more bad stuff. We need a new broadcaster....
+# frozen_string_literal: true
+
+# Broadcast shim: provides broadcast_supplier / broadcast_user to all
+# SimplyStored::Couch models without requiring ApplicationController.new.
+#
+# PREVIOUSLY (dangerous):
+#   ApplicationController.new.send(:broadcast_supplier, *args)
+#   → leaked controller instances, no request lifecycle
+#
+# NOW:
+#   Delegates directly to Mozo.broadcast_supplier / Mozo.broadcast_user
+#   which uses Mozo.broadcaster (configurable: Faye or ActionCable).
+#
+# MIGRATION PATH:
+#   Models should `include Broadcastable` directly instead of relying
+#   on this monkey-patch. Once all models include Broadcastable, this
+#   initializer can be removed.
+#
 require 'simply_stored/couch'
+
 module ModelBroadcast
-  def broadcast_supplier(*args)
-    ApplicationController.new.send(:broadcast_supplier, *args)
+  def broadcast_supplier(sid, event, data = {})
+    Mozo.broadcast_supplier(sid, event, data)
   end
-  def broadcast_user(*args)
-    ApplicationController.new.send(:broadcast_user, *args)
+
+  def broadcast_user(uid, event, data = {})
+    Mozo.broadcast_user(uid, event, data)
   end
 end
+
 SimplyStored::Couch.send(:include, ModelBroadcast)
-#SimplyStored::Couch.send(:extend, ModelBroadcast) # this should never happen!!!