Consume the durable message-feedback sidecar from #2217 in the browser:
per-message Like/Dislike with an optional note, contributed through a
declared assistant-actions slot.
- carry MessageId on finalized AssistantMessageNode so a target is nameable
- declare conversation.chat.assistant-actions and render it in the
IconActions row between copy and branch
- hold one FeedbackController per Session with per-item ifVersion CAS,
reconciling a version-conflict from the reply's authoritative item
- mount messageFeedbackRemote alongside goalsRemote
