feat(feedback): add the Web surface for message feedback

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

packages/bundle/web-app/package.json

@@ -56,6 +56,7 @@
     "@deepseek-ai/dsh-client-ui-command": "workspace:^",
     "@deepseek-ai/dsh-client-ui-conversation": "workspace:^",
     "@deepseek-ai/dsh-client-ui-deliverables": "workspace:^",
+    "@deepseek-ai/dsh-client-ui-feedback": "workspace:^",
     "@deepseek-ai/dsh-client-ui-goal": "workspace:^",
     "@deepseek-ai/dsh-client-ui-layout": "workspace:^",
     "@deepseek-ai/dsh-client-ui-model": "workspace:^",