feat(attendance,elective): 考勤与选修课模块审计重构 — P0 修复 + i18n + Error Boundary

审计报告：docs/architecture/audit/attendance-elective-audit-report.md

P0 修复：
- attendance: getAttendanceStats 统计失真（仅基于前 20 条记录）改为 SQL 聚合查询
- attendance: getClassStudentsForAttendance 跨模块直查 classEnrollments 改为调用 classes data-access
- attendance: update/delete Action 新增资源归属校验（assertRecordOwnership）
- elective: update/delete/openSelection/closeSelection/runLottery Action 新增资源归属校验（assertCourseOwnership）

i18n 接入：
- 新增 attendance/elective 命名空间（zh-CN + en）
- attendance-stats-cards 接入 useTranslations
- elective-course-list/form 接入 useTranslations

类型安全（P1）：
- elective-course-form: 移除 as 断言，改用类型守卫 isSelectionMode
- elective-course-list: 移除 null as never 类型逃逸，改用泛型

Error Boundary：
- 新增 admin/teacher attendance error.tsx
- 新增 admin/student elective error.tsx

架构图同步：
- 004: 修正 attendance/elective/parent 章节的导出函数、文件清单、已知问题
- 005: 修正 actions 的 usedBy（标记无调用方的死代码）、新增 issues 字段、更新依赖矩阵

src/app/(dashboard)/admin/attendance/error.tsx

@@ -0,0 +1,24 @@
+"use client"
+
+import { AlertCircle } from "lucide-react"
+import { useTranslations } from "next-intl"
+
+import { EmptyState } from "@/shared/components/ui/empty-state"
+
+export default function AdminAttendanceError({ reset }: { error: Error & { digest?: string }; reset: () => void }) {
+  const t = useTranslations("attendance")
+  return (
+    <div className="flex h-full flex-col items-center justify-center space-y-4 p-8">
+      <EmptyState
+        icon={AlertCircle}
+        title={t("errors.unexpected")}
+        description={t("errors.unexpected")}
+        action={{
+          label: t("actions.save"),
+          onClick: () => reset(),
+        }}
+        className="border-none shadow-none h-auto"
+      />
+    </div>
+  )
+}

src/app/(dashboard)/admin/elective/error.tsx

@@ -0,0 +1,24 @@
+"use client"
+
+import { AlertCircle } from "lucide-react"
+import { useTranslations } from "next-intl"
+
+import { EmptyState } from "@/shared/components/ui/empty-state"
+
+export default function AdminElectiveError({ reset }: { error: Error & { digest?: string }; reset: () => void }) {
+  const t = useTranslations("elective")
+  return (
+    <div className="flex h-full flex-col items-center justify-center space-y-4 p-8">
+      <EmptyState
+        icon={AlertCircle}
+        title={t("errors.unexpected")}
+        description={t("errors.unexpected")}
+        action={{
+          label: t("actions.save"),
+          onClick: () => reset(),
+        }}
+        className="border-none shadow-none h-auto"
+      />
+    </div>
+  )
+}