refactor(admin): A2UI 双轨收敛,统一 artifact 协议

- mergeArtifactIntoMessage 不再派发 legacy 列表,只维护 uiArtifacts
- 渲染层从 uiArtifacts 派生 forms/reviews/charts,为空时回退 legacy
  (历史消息兼容,老 metadata 仅 a2uiForm/a2uiReview/a2uiChart)
- sseReducer 删除 ui.form/ui.review/ui.chart 旧事件分支,只消费
  ui.artifact(后端过渡期双发,旧事件将被忽略)
- types.ts legacy 字段标注 deprecated;契约文档同步现状
- 测试更新:旧事件忽略 + uiArtifacts 合并/恢复断言

aislop scan: 5 引擎 0 issues

apps/admin/src/components/AiChat/message-mappers.integration.test.ts

@@ -78,7 +78,7 @@ describe('AI chat history mapper', () => {
     expect(mapped.message.forms?.[0]).toMatchObject({ id: 'form-9', title: '新增学生' });
   });
 
-  it('restores uiArtifacts from message metadata and derives legacy lists', () => {
+  it('restores uiArtifacts from message metadata (统一协议)', () => {
     const mapped = mapHistoryMessage({
       id: 8,
       role: 'assistant',
@@ -120,8 +120,14 @@ describe('AI chat history mapper', () => {
     });
 
     expect(mapped.message.uiArtifacts).toHaveLength(2);
-    expect(mapped.message.forms?.[0]).toMatchObject({ id: 'form-10', status: 'submitted' });
-    expect(mapped.message.reviews?.[0]).toMatchObject({ id: 'review-10', status: 'expired' });
+    expect(mapped.message.uiArtifacts?.[0].payload).toMatchObject({
+      id: 'form-10',
+      status: 'submitted',
+    });
+    expect(mapped.message.uiArtifacts?.[1].payload).toMatchObject({
+      id: 'review-10',
+      status: 'expired',
+    });
   });
 
   it('restores a persisted A2UI review from message metadata', () => {