feat(attendance,elective): 实现所有 P2 长期改进项

P2 修复（来自审计报告）：
- 2.4.4: Server Action 错误消息 i18n 化（attendance/elective 全部 Action）
- 2.5.3: 抽取 AttendancePageLayout 组件复用（admin/teacher 页面）
- 2.5.4: 抽取 ElectivePageLayout 组件复用（admin/teacher 列表页）
- 2.6.3: 考勤月历键盘导航（tabIndex + 方向键 + Home/End + role=grid）
- 2.8.2: getStudentAttendanceSummary 分页优化（SQL 聚合统计 + LIMIT 分页）
- 2.8.3: resolveCourseDisplayNames 缓存优化（React cache 去重）
- 2.1.4: elective data-access 跨模块依赖接口抽象（resolvers.ts 可注入）

P2 建议项：
- 选课时间冲突检测（parseSchedule + isScheduleConflict 纯函数 + checkScheduleConflict）
- 学分上限校验（MAX_CREDIT_PER_TERM + checkCreditLimit）
- 考勤/选课数据导出 Excel（export.ts + API 路由扩展）

新增文件：
- src/modules/attendance/components/attendance-page-layout.tsx
- src/modules/elective/components/elective-page-layout.tsx
- src/modules/elective/resolvers.ts
- src/modules/attendance/export.ts
- src/modules/elective/export.ts

校验：
- npm run lint 通过（exit 0）
- npx tsc --noEmit attendance/elective/parent 相关零错误

src/modules/attendance/data-access-stats.ts

@@ -1,9 +1,10 @@
 import "server-only"
 
-import { and, asc, desc, eq, gte, lte } from "drizzle-orm"
+import { and, asc, count, desc, eq, gte, lte, sql } from "drizzle-orm"
 
 import { db } from "@/shared/db"
 import { attendanceRecords, classes, users } from "@/shared/db/schema"
+import { safeParseDate } from "@/shared/lib/action-utils"
 
 import type {
   AttendanceListItem,
@@ -23,6 +24,9 @@ const EMPTY_STATS: AttendanceStats = {
   lateRate: 0,
 }
 
+/** 最近记录的默认截取数量（避免一次拉全量） */
+const DEFAULT_RECENT_LIMIT = 20
+
 /**
  * 根据考勤记录行计算统计（纯函数，便于测试）。
  */
@@ -41,13 +45,44 @@ export const computeStats = (rows: { status: string }[]): AttendanceStats => {
   return stats
 }
 
+/**
+ * 将 SQL 聚合行转换为 AttendanceStats（避免拉全量记录计算统计）。
+ */
+const statsFromAggregate = (row: {
+  total: number
+  present: number
+  absent: number
+  late: number
+  earlyLeave: number
+  excused: number
+}): AttendanceStats => {
+  const total = Number(row.total ?? 0)
+  const present = Number(row.present ?? 0)
+  const late = Number(row.late ?? 0)
+  return {
+    total,
+    present,
+    absent: Number(row.absent ?? 0),
+    late,
+    earlyLeave: Number(row.earlyLeave ?? 0),
+    excused: Number(row.excused ?? 0),
+    presentRate: total > 0 ? Math.round((present / total) * 10000) / 100 : 0,
+    lateRate: total > 0 ? Math.round((late / total) * 10000) / 100 : 0,
+  }
+}
+
 const serializeDate = (d: Date | string | null): string =>
   d ? new Date(d).toISOString().slice(0, 10) : ""
 
+/**
+ * 获取学生考勤汇总。
+ * 优化：统计使用 SQL 聚合查询（避免拉全量记录），最近记录使用 LIMIT 分页。
+ */
 export async function getStudentAttendanceSummary(
   studentId: string,
   startDate?: string,
-  endDate?: string
+  endDate?: string,
+  recentLimit: number = DEFAULT_RECENT_LIMIT
 ): Promise<StudentAttendanceSummary | null> {
   const [student] = await db
     .select({ name: users.name })
@@ -57,9 +92,33 @@ export async function getStudentAttendanceSummary(
   if (!student) return null
 
   const conditions = [eq(attendanceRecords.studentId, studentId)]
-  if (startDate) conditions.push(gte(attendanceRecords.date, new Date(startDate)))
-  if (endDate) conditions.push(lte(attendanceRecords.date, new Date(endDate)))
+  if (startDate) conditions.push(gte(attendanceRecords.date, safeParseDate(startDate, "开始日期")))
+  if (endDate) conditions.push(lte(attendanceRecords.date, safeParseDate(endDate, "结束日期")))
+  const where = and(...conditions)
 
+  // 统计使用 SQL 聚合，避免拉全量记录
+  const [statsRow] = await db
+    .select({
+      total: count(),
+      present: sql<number>`COALESCE(SUM(CASE WHEN ${attendanceRecords.status} = 'present' THEN 1 ELSE 0 END), 0)`,
+      absent: sql<number>`COALESCE(SUM(CASE WHEN ${attendanceRecords.status} = 'absent' THEN 1 ELSE 0 END), 0)`,
+      late: sql<number>`COALESCE(SUM(CASE WHEN ${attendanceRecords.status} = 'late' THEN 1 ELSE 0 END), 0)`,
+      earlyLeave: sql<number>`COALESCE(SUM(CASE WHEN ${attendanceRecords.status} = 'early_leave' THEN 1 ELSE 0 END), 0)`,
+      excused: sql<number>`COALESCE(SUM(CASE WHEN ${attendanceRecords.status} = 'excused' THEN 1 ELSE 0 END), 0)`,
+    })
+    .from(attendanceRecords)
+    .where(where)
+
+  const stats = statsFromAggregate(statsRow ?? {
+    total: 0,
+    present: 0,
+    absent: 0,
+    late: 0,
+    earlyLeave: 0,
+    excused: 0,
+  })
+
+  // 最近记录使用 LIMIT 分页，避免拉全量
   const rows = await db
     .select({
       record: attendanceRecords,
@@ -67,12 +126,11 @@ export async function getStudentAttendanceSummary(
     })
     .from(attendanceRecords)
     .leftJoin(classes, eq(classes.id, attendanceRecords.classId))
-    .where(and(...conditions))
+    .where(where)
     .orderBy(desc(attendanceRecords.date))
+    .limit(recentLimit)
 
-  const stats = computeStats(rows.map((r) => ({ status: r.record.status })))
-
-  const recentRecords: AttendanceListItem[] = rows.slice(0, 20).map((r) => ({
+  const recentRecords: AttendanceListItem[] = rows.map((r) => ({
     id: r.record.id,
     studentId: r.record.studentId,
     studentName: student.name ?? "Unknown",
@@ -108,8 +166,8 @@ export async function getClassAttendanceStats(
   if (!classRow) return null
 
   const conditions = [eq(attendanceRecords.classId, classId)]
-  if (startDate) conditions.push(gte(attendanceRecords.date, new Date(startDate)))
-  if (endDate) conditions.push(lte(attendanceRecords.date, new Date(endDate)))
+  if (startDate) conditions.push(gte(attendanceRecords.date, safeParseDate(startDate, "开始日期")))
+  if (endDate) conditions.push(lte(attendanceRecords.date, safeParseDate(endDate, "结束日期")))
 
   const rows = await db
     .select({