feat: Excel 导入预检与动态问答，AI 聊天/文件解析体验修复

- imports: 新增 preflight_import 预检报告（判定/分阶段统计/阻断归因/问题/下一步/错误示例），导入任务 settings 落库（映射/校区/更新/重复/未匹配策略），预览应用策略，向导提交写操作日志
- ai-chat: 新增 excel_analyze（ExcelJS）工具，移除附件/上下文截断，start_import_wizard 支持确认参数，ui.import_preflight SSE，预览确认写操作日志
- admin: ImportPreflightCard 渲染与持久化，聊天抽屉布局/侧边栏修复，考勤页 CSS 引入，费用/学生页接口 schema 校验修复

apps/admin/src/components/AiChat/provider.integration.test.ts

@@ -154,6 +154,47 @@ describe('AI chat SSE message reducer', () => {
     expect(message.forms?.[1]).toMatchObject({ id: 'form-2' });
   });
 
+  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, {
       event: 'message.completed',