fix(ai): 清理 aislop 扫描告警

- 拆分 SSE reducer 到 sseReducer.ts，provider.ts 降至 220 行
- artifact 合并工具抽到 uiArtifacts.ts，去除双重类型断言
- 业务上下文注册表改用 field/relation/entity 构建器收敛重复
- aislop 分数 71 → 81（Healthy），AI Slop 0 告警

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

@@ -9,7 +9,7 @@ import type {
   AiReviewSchema,
   AiToolRun,
 } from './types';
-import { mergeArtifactIntoMessage } from './provider';
+import { mergeArtifactIntoMessage } from './uiArtifacts';
 
 function mapStatus(record: AiMessageRecord): AiChatMessageStatus {
   if (record.status === 'pending') return 'loading';