refactor(attendance,elective): 审计第二轮 — 全量完成 P0/P1 改进项

P0 修复：
- 页面层 i18n 全量补齐（admin/teacher/parent/student × attendance/elective）
- types.ts 状态标签常量迁移至 constants.ts（i18n key + Badge variant）
- 修复 getTranslations 导入路径（next-intl → next-intl/server）

P1 改进：
- 解耦 parent 模块对 attendance 类型的直接依赖（本地 view-model 类型）
- 导出纯函数（computeStats/buildWarnings/buildLotteryRankCase 等）
- 统一空状态为 EmptyState 组件
- 清理死代码读 Action（attendance 5 个 + elective 3 个）
- 预留监控埋点接口（trackEvent 13 个新事件名）
- 补齐骨架屏 loading.tsx（8 个页面）
- AlertDialog 替换 window.confirm（student-selection-view）
- a11y 改进（aria-label/role/键盘导航）

修复：
- AttendanceStatus 从 constants.ts 重导出，消除 types/constants 双源混乱
- buildWarnings 的 Translator 类型改用 ReturnType<typeof useTranslations>

src/app/(dashboard)/student/elective/page.tsx

@@ -1,23 +1,19 @@
+import { getTranslations } from "next-intl/server"
 import { getAuthContext } from "@/shared/lib/auth-guard"
 
 import { getAvailableCoursesForStudent, getStudentSelections } from "@/modules/elective/data-access-selections"
 import { StudentSelectionView } from "@/modules/elective/components/student-selection-view"
 import { ElectiveFilters } from "@/modules/elective/components/elective-filters"
+import { getParam, type SearchParams } from "@/shared/lib/search-params"
 
 export const dynamic = "force-dynamic"
 
-type SearchParams = { [key: string]: string | string[] | undefined }
-
-const getParam = (params: SearchParams, key: string) => {
-  const v = params[key]
-  return Array.isArray(v) ? v[0] : v
-}
-
 export default async function StudentElectivePage({
   searchParams,
 }: {
   searchParams: Promise<SearchParams>
 }) {
+  const t = await getTranslations("elective")
   const ctx = await getAuthContext()
   const studentId = ctx.userId
 
@@ -39,10 +35,8 @@ export default async function StudentElectivePage({
   return (
     <div className="space-y-8">
       <div>
-        <h2 className="text-2xl font-bold tracking-tight">Elective Courses</h2>
-        <p className="text-muted-foreground">
-          Browse available electives and manage your selections.
-        </p>
+        <h2 className="text-2xl font-bold tracking-tight">{t("title.student")}</h2>
+        <p className="text-muted-foreground">{t("description.student")}</p>
       </div>
       {availableCourses.length > 0 && <ElectiveFilters />}
       <StudentSelectionView