fix(action_cable): use Redis adapter in development too

- async adapter is in-process — works in Puma request cycle
  but fails from Rails console (no event loop to deliver messages)
- Redis is shared-state, works from any context (console, jobs, requests)
- Dev uses Redis DB 2, separate channel_prefix from production

config/cable.yml

@@ -6,7 +6,9 @@
 #                Redis is also used for Mozo::Counter (replacing DrbCounter).
 #
 development:
-  adapter: async
+  adapter: redis
+  url: <%= ENV.fetch("REDIS_URL") { "redis://localhost:6379/2" } %>
+  channel_prefix: mozo_backend_dev
 
 test:
   adapter: test