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/provider.integration.test.ts

@@ -189,46 +189,6 @@ describe('AI chat SSE message reducer', () => {
     expect(message.reviews?.[0]).toMatchObject({ id: 'review-1', status: 'expired' });
   });
 
-  it('stores ui.import_preflight in message metadata and restores it from completed message', () => {
-    const preflight = {
-      verdict: 'needs_input',
-      stages: [
-        {
-          stepKey: 'students',
-          label: '学生档案',
-          sheetNames: ['学生'],
-          total: 2,
-          create: 1,
-          update: 1,
-          error: 0,
-          skip: 0,
-          mapping: { name: '姓名' },
-          missingRequired: [],
-        },
-      ],
-      blocks: [],
-      questions: [{ key: 'update', type: 'update', label: '文件中有 1 行已匹配现有记录' }],
-      nextSteps: [{ key: 'students-next', label: '分班 / 排课 / 入住', description: '建议', after: ['students'] }],
-    };
-    let message = reduceAiSseMessage(undefined, {
-      event: 'ui.import_preflight',
-      data: JSON.stringify({ messageId: 8, preflight }),
-    });
-    expect(message.metadata?.a2uiImportPreflight).toEqual(preflight);
-
-    message = reduceAiSseMessage(message, {
-      event: 'message.completed',
-      data: JSON.stringify({
-        message: {
-          id: 8,
-          content: '预检完成',
-          status: 'completed',
-          metadata: { a2uiImportPreflight: preflight },
-        },
-      }),
-    });
-    expect(message.metadata?.a2uiImportPreflight).toEqual(preflight);
-  });
 
   it('restores a persisted form from message.completed metadata', () => {
     const message = reduceAiSseMessage(undefined, {