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/parent/components/parent-attendance-calendar.tsx

@@ -1,7 +1,7 @@
 "use client"
 
 import { ChevronLeft, ChevronRight } from "lucide-react"
-import { useState } from "react"
+import { useState, useRef, type KeyboardEvent } from "react"
 import { useTranslations } from "next-intl"
 
 import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
@@ -78,6 +78,7 @@ export function isSameDay(a: Date, b: Date): boolean {
 /**
  * 家长视角的考勤月历视图。
  * 基于子女的近期考勤记录，在月历上按状态着色，让家长直观看到出勤分布。
+ * 支持键盘方向键导航（a11y）：← → ↑ ↓ 在日期格子间移动，Home/End 跳至行首/尾。
  */
 export function ParentAttendanceCalendar({
   summary,
@@ -88,6 +89,8 @@ export function ParentAttendanceCalendar({
   const now = new Date()
   const [viewYear, setViewYear] = useState(now.getFullYear())
   const [viewMonth, setViewMonth] = useState(now.getMonth())
+  const [focusedIdx, setFocusedIdx] = useState<number>(-1)
+  const gridRef = useRef<HTMLDivElement>(null)
 
   const recordMap = new Map<string, ParentAttendanceListItem>()
   for (const r of summary.recentRecords) {
@@ -108,6 +111,7 @@ export function ParentAttendanceCalendar({
     } else {
       setViewMonth((m) => m - 1)
     }
+    setFocusedIdx(-1)
   }
   const goNext = () => {
     if (viewMonth === 11) {
@@ -116,6 +120,60 @@ export function ParentAttendanceCalendar({
     } else {
       setViewMonth((m) => m + 1)
     }
+    setFocusedIdx(-1)
+  }
+
+  /**
+   * 键盘导航：方向键在日期格子间移动，Home/End 跳至行首/尾。
+   * 仅在非空格子（有 Date 的格子）间移动，跳过 null 占位。
+   */
+  const handleKeyDown = (e: KeyboardEvent<HTMLDivElement>) => {
+    if (focusedIdx < 0) return
+    const nonNullIndices = days
+      .map((d, i) => (d ? i : -1))
+      .filter((i) => i >= 0)
+    const currentPos = nonNullIndices.indexOf(focusedIdx)
+    if (currentPos < 0) return
+
+    const cols = 7
+    const currentRow = Math.floor(currentPos / cols)
+    const currentCol = currentPos % cols
+    let nextPos = currentPos
+
+    switch (e.key) {
+      case "ArrowRight":
+        nextPos = Math.min(currentPos + 1, nonNullIndices.length - 1)
+        break
+      case "ArrowLeft":
+        nextPos = Math.max(currentPos - 1, 0)
+        break
+      case "ArrowDown": {
+        const target = (currentRow + 1) * cols + currentCol
+        nextPos = target < nonNullIndices.length ? target : currentPos
+        break
+      }
+      case "ArrowUp": {
+        const target = (currentRow - 1) * cols + currentCol
+        nextPos = target >= 0 ? target : currentPos
+        break
+      }
+      case "Home":
+        nextPos = currentRow * cols
+        break
+      case "End":
+        nextPos = Math.min((currentRow + 1) * cols - 1, nonNullIndices.length - 1)
+        break
+      default:
+        return
+    }
+
+    e.preventDefault()
+    const nextIdx = nonNullIndices[nextPos]
+    if (nextIdx !== undefined && nextIdx !== focusedIdx) {
+      setFocusedIdx(nextIdx)
+      const cell = gridRef.current?.querySelector<HTMLElement>(`[data-day-idx="${nextIdx}"]`)
+      cell?.focus()
+    }
   }
 
   const usedStatuses = new Set<ParentAttendanceStatus>()
@@ -155,26 +213,39 @@ export function ParentAttendanceCalendar({
             </div>
           ))}
         </div>
-        <div className="grid grid-cols-7 gap-1">
+        <div
+          ref={gridRef}
+          className="grid grid-cols-7 gap-1"
+          onKeyDown={handleKeyDown}
+          role="grid"
+          aria-label={monthLabel}
+        >
           {days.map((d, idx) => {
             if (!d) return <div key={`empty-${idx}`} className="aspect-square" />
             const key = formatDateKey(d)
             const record = recordMap.get(key)
             const isToday = isSameDay(d, now)
+            const isFocused = focusedIdx === idx
             return (
               <div
                 key={key}
+                data-day-idx={idx}
+                tabIndex={isFocused || (focusedIdx < 0 && isToday) ? 0 : -1}
+                onFocus={() => setFocusedIdx(idx)}
                 className={cn(
                   "relative flex aspect-square flex-col items-center justify-center rounded-md border text-xs",
-                  "min-h-[36px]",
+                  "min-h-[36px] cursor-default",
                   record ? "border-border bg-muted/30" : "border-transparent",
                   isToday && "ring-2 ring-primary ring-offset-1",
+                  "focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2",
                 )}
+                role="gridcell"
                 aria-label={
                   record
                     ? `${formatDateKey(d)}: ${t(ATTENDANCE_STATUS_LABEL_KEYS[record.status])}`
                     : formatDateKey(d)
                 }
+                aria-selected={isFocused}
               >
                 <span className="tabular-nums">{d.getDate()}</span>
                 {record ? (