feat(ai): 移除 Excel 导入预检链路

- 删除 preflight_import 工具、预检卡、resolve 接口与 ui.import_preflight 事件
- 删除 imports.preflight 解析器与 PreflightReport 类型
- SYSTEM_PROMPT 改为上传 Excel 后直接确认列映射/策略并调用 start_import_wizard
- 前端同步移除预检类型/组件/测试，保留导入向导

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

@@ -186,25 +186,4 @@ describe('AI chat history mapper', () => {
     expect(mapped.message.charts?.[0]).toMatchObject({ id: 'chart-9', chartType: 'bar' });
   });
 
-  it('keeps import preflight metadata on history messages', () => {
-    const preflight = {
-      verdict: 'needs_input',
-      stages: [],
-      blocks: [],
-      questions: [{ key: 'update', type: 'update', label: '文件中有 1 行已匹配现有记录' }],
-      nextSteps: [],
-    };
-    const mapped = mapHistoryMessage({
-      id: 8,
-      role: 'assistant',
-      content: '预检完成',
-      reasoningContent: null,
-      status: 'completed',
-      errorCode: null,
-      createdAt: '2026-07-23T00:00:00.000Z',
-      metadata: { a2uiImportPreflight: preflight },
-    });
-
-    expect(mapped.message.metadata?.a2uiImportPreflight).toEqual(preflight);
-  });
 });