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

apps/web/tests/snapshots/goal-multi-turn-actions/ui.expected.md

@@ -77,6 +77,10 @@
 - paragraph: 这是一个很典型的轻量 TypeScript 包结构：入口 + 实现 + 测试。这一轮到此结束，等系统开启下一个 turn。
 - button "Copy":
   - img
+- button "Good response":
+  - img
+- button "Bad response":
+  - img
 - button "Branch into a new conversation":
   - img
 - text: {{clock}} Ran for {{duration}} TTFT {{duration}} {{throughput}} tok/s
@@ -186,6 +190,10 @@
   - text: ）的结构，或者其他格式的输出（比如带文件大小的树形图），随时告诉我。
 - button "Copy":
   - img
+- button "Good response":
+  - img
+- button "Bad response":
+  - img
 - button "Branch into a new conversation":
   - img
 - tooltip "Branch into a new conversation"