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/server/src/imports/imports.preview.service.ts

@@ -8,6 +8,7 @@ import { IMPORT_STEP_LABELS } from './imports.types';
 import type {
   CellValue,
   ColumnMapping,
+  ImportRunSettings,
   ImportStepKey,
   StepPreviewSummary,
 } from './imports.types';
@@ -16,6 +17,7 @@ import { assertMapping, suggestMapping } from './imports.mapping';
 import { buildLookups } from './imports.lookups';
 import { validateRow } from './imports.rows';
 import type { ImportBatchState } from './imports.rows';
+import { applyPreviewPolicies } from './imports.policies';
 import { findOwnedRun, findStep } from './imports.access';
 import type { ImportPrincipal } from './imports.access';
 
@@ -55,6 +57,7 @@ export class ImportPreviewService {
     const sheetsData =
       parseJson<Array<{ name: string; headers: string[]; rows: CellValue[][] }>>(run.sheetsJson) ??
       [];
+    const settings = parseJson<ImportRunSettings>(run.settingsJson) ?? {};
     const sheetNames = body.sheets?.length
       ? body.sheets
       : (parseJson<string[]>(step.sheetsJson) ?? []);
@@ -106,20 +109,22 @@ export class ImportPreviewService {
           fields[field] = rawValues[sheet.headers.indexOf(header)] ?? null;
         }
         const result = validateRow(stepKey, fields, lookups, batchState);
+        const policy = applyPreviewPolicies(result, settings);
         const normalized = { ...result.normalized, ...result.resolvedIds };
         summary.total += 1;
-        if (result.errors.length > 0) {
+        if (policy.status === 'error') {
           summary.error += 1;
         } else {
           summary.valid += 1;
-          if (result.action === 'create') summary.create += 1;
-          if (result.action === 'update') summary.update += 1;
-          if (result.action === 'create') {
-            const studentId = result.resolvedIds._studentId;
-            if (studentId !== undefined) {
-              if (stepKey === 'checkins') batchState.checkinStudentIds.add(studentId);
-              if (stepKey === 'transfers') batchState.transferStudentIds.add(studentId);
-            }
+          if (policy.action === 'create') summary.create += 1;
+          if (policy.action === 'update') summary.update += 1;
+          if (policy.action === 'skip') summary.skip += 1;
+        }
+        if (policy.status === 'valid' && policy.action === 'create') {
+          const studentId = result.resolvedIds._studentId;
+          if (studentId !== undefined) {
+            if (stepKey === 'checkins') batchState.checkinStudentIds.add(studentId);
+            if (stepKey === 'transfers') batchState.transferStudentIds.add(studentId);
           }
         }
         rowEntities.push(
@@ -131,9 +136,9 @@ export class ImportPreviewService {
             rawJson: JSON.stringify(raw),
             normalizedJson: JSON.stringify(normalized),
             matchKey: result.matchKey,
-            action: result.action,
-            status: result.errors.length > 0 ? 'error' : 'valid',
-            errorsJson: result.errors.length > 0 ? JSON.stringify(result.errors) : null,
+            action: policy.action,
+            status: policy.status,
+            errorsJson: policy.errors.length > 0 ? JSON.stringify(policy.errors) : null,
             targetId: result.targetId ?? null,
           }),
         );