Create ActionCable channel for guest chat subscriptions

## Task Create an ActionCable channel that allows unauthenticated guests to subscribe to chat messages for their support session. ## Why ActionCable? - Guests have no NATS device/authentication - Need WebSocket for real-time without polling - ActionCable is already available in Rails stack - Can authenticate via session token in connection params ## Channel Design ```ruby # app/channels/support_session_chat_channel.rb class SupportSessionChatChannel < ApplicationCable::Channel def subscribed session = find_session_by_token(params[:token]) if session&.can_join? stream_from "support_session_chat:#{session.id}" @session = session else reject end end def unsubscribed stop_all_streams end def receive(data) # Handle incoming messages from WebSocket # Validate and save via SendChatMessageService end end ``` ## Connection Authentication Modify `ApplicationCable::Connection` to support token-based auth for guests (in addition to existing user auth). ## Broadcast Integration Update `SendChatMessageService` to broadcast via: ```ruby ActionCable.server.broadcast( "support_session_chat:#{session.id}", message.to_broadcast_payload ) ``` ## Files to Create/Modify - `app/channels/support_session_chat_channel.rb` - `app/channels/application_cable/connection.rb` (modify for guest tokens) - `spec/channels/support_session_chat_channel_spec.rb`