[andypalmi]

Description

1. Chat requests, aborts, votes, system notices and the answers to the agent's in-flight requests are sent by a chat publisher (frontend/src/publishers/expert-chat.publisher.ts) built on the team publisher contract, instead of from the product-expert store.
2. The publisher shares the agent's connection with the chat subscriber and keeps the session it connected with. A send while disconnected fails instead of being dropped.
3. The team publisher contract gains the same connection key and credentials hooks as the subscriber one.
4. The store connects and disconnects both and no longer holds MQTT code. Turn tracking and the send queue stay in the store, since they are chat state rather than transport.

Related Issue(s)

Closes #9030

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.
  • Not needed: no user-facing change.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.62%. Comparing base (d7cac90) to head (2848f75).

Additional details and impacted files

@@                       Coverage Diff                        @@
##           refactor/expert-chat-subscriber    #9073   +/-   ##
================================================================
  Coverage                            79.61%   79.62%           
================================================================
  Files                                  475      475           
  Lines                                26086    26086           
  Branches                              6954     6954           
================================================================
+ Hits                                 20769    20770    +1     
+ Misses                                5317     5316    -1     

Flag	Coverage Δ
backend	79.62% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.