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/modules/elective/components/student-selection-view.tsx

@@ -3,19 +3,32 @@
 import { useState, useTransition } from "react"
 import { useRouter } from "next/navigation"
 import { toast } from "sonner"
+import { useTranslations } from "next-intl"
 import { BookOpen, CheckCircle2, XCircle } from "lucide-react"
 
+import {
+  AlertDialog,
+  AlertDialogAction,
+  AlertDialogCancel,
+  AlertDialogContent,
+  AlertDialogDescription,
+  AlertDialogFooter,
+  AlertDialogHeader,
+  AlertDialogTitle,
+  AlertDialogTrigger,
+} from "@/shared/components/ui/alert-dialog"
 import { Badge } from "@/shared/components/ui/badge"
 import { Button } from "@/shared/components/ui/button"
 import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
 import { EmptyState } from "@/shared/components/ui/empty-state"
 
 import {
-  COURSE_SELECTION_STATUS_COLORS,
-  COURSE_SELECTION_STATUS_LABELS,
-  ELECTIVE_STATUS_LABELS,
-  SELECTION_MODE_LABELS,
-} from "../types"
+  COURSE_SELECTION_STATUS_BADGE_VARIANTS,
+  COURSE_SELECTION_STATUS_LABEL_KEYS,
+  ELECTIVE_STATUS_BADGE_VARIANTS,
+  ELECTIVE_STATUS_LABEL_KEYS,
+  SELECTION_MODE_LABEL_KEYS,
+} from "../constants"
 import type {
   CourseSelectionWithDetails,
   ElectiveCourseWithDetails,
@@ -30,6 +43,7 @@ export function StudentSelectionView({
   mySelections: CourseSelectionWithDetails[]
 }) {
   const router = useRouter()
+  const t = useTranslations("elective")
   const [pendingId, setPendingId] = useState<string | null>(null)
   const [isPending, startTransition] = useTransition()
 
@@ -47,10 +61,10 @@ export function StudentSelectionView({
       formData.set("courseId", courseId)
       const res = await selectCourseAction(null, formData)
       if (res.success) {
-        toast.success(res.message)
+        toast.success(res.message || t("student.selectSuccess"))
         router.refresh()
       } else {
-        toast.error(res.message ?? "Failed to select course")
+        toast.error(res.message ?? t("errors.unexpected"))
       }
       setPendingId(null)
     })
@@ -63,10 +77,10 @@ export function StudentSelectionView({
       formData.set("courseId", courseId)
       const res = await dropCourseAction(null, formData)
       if (res.success) {
-        toast.success(res.message)
+        toast.success(res.message || t("student.dropSuccess"))
         router.refresh()
       } else {
-        toast.error(res.message ?? "Failed to drop course")
+        toast.error(res.message ?? t("errors.unexpected"))
       }
       setPendingId(null)
     })
@@ -76,15 +90,15 @@ export function StudentSelectionView({
     <div className="space-y-8">
       <section className="space-y-4">
         <div className="flex items-center justify-between">
-          <h3 className="text-lg font-semibold">My Selections</h3>
+          <h3 className="text-lg font-semibold">{t("student.mySelections")}</h3>
           <span className="text-sm text-muted-foreground">
-            {activeSelections.length} active
+            {activeSelections.length}
           </span>
         </div>
         {activeSelections.length === 0 ? (
           <EmptyState
-            title="No selections yet"
-            description="Browse available courses below and select your electives."
+            title={t("list.empty")}
+            description={t("description.student")}
             icon={BookOpen}
             className="h-auto border-none shadow-none"
           />
@@ -94,33 +108,52 @@ export function StudentSelectionView({
               <Card key={sel.id}>
                 <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
                   <CardTitle className="text-base">
-                    {sel.courseName ?? "Unknown course"}
+                    {sel.courseName ?? t("errors.notFound")}
                   </CardTitle>
-                  <Badge variant={COURSE_SELECTION_STATUS_COLORS[sel.status]}>
-                    {COURSE_SELECTION_STATUS_LABELS[sel.status]}
+                  <Badge variant={COURSE_SELECTION_STATUS_BADGE_VARIANTS[sel.status]}>
+                    {t(COURSE_SELECTION_STATUS_LABEL_KEYS[sel.status])}
                   </Badge>
                 </CardHeader>
                 <CardContent className="space-y-3">
                   {sel.courseCapacity !== null && sel.courseEnrolledCount !== null ? (
                     <p className="text-xs text-muted-foreground">
-                      Enrolled: {sel.courseEnrolledCount}/{sel.courseCapacity}
+                      {t("fields.enrolled")}: {sel.courseEnrolledCount}/{sel.courseCapacity}
                     </p>
                   ) : null}
                   {sel.lotteryRank ? (
                     <p className="text-xs text-muted-foreground">
-                      Lottery rank: #{sel.lotteryRank}
+                      #{sel.lotteryRank}
                     </p>
                   ) : null}
-                  <Button
-                    variant="outline"
-                    size="sm"
-                    className="text-destructive hover:text-destructive"
-                    disabled={isPending && pendingId === sel.courseId}
-                    onClick={() => handleDrop(sel.courseId)}
-                  >
-                    <XCircle className="mr-1 h-3 w-3" />
-                    Drop
-                  </Button>
+                  <AlertDialog>
+                    <AlertDialogTrigger asChild>
+                      <Button
+                        variant="outline"
+                        size="sm"
+                        className="text-destructive hover:text-destructive"
+                        disabled={isPending && pendingId === sel.courseId}
+                      >
+                        <XCircle className="mr-1 h-3 w-3" />
+                        {t("actions.drop")}
+                      </Button>
+                    </AlertDialogTrigger>
+                    <AlertDialogContent>
+                      <AlertDialogHeader>
+                        <AlertDialogTitle>{t("student.confirmDrop")}</AlertDialogTitle>
+                        <AlertDialogDescription>
+                          {t("student.confirmDrop")}
+                        </AlertDialogDescription>
+                      </AlertDialogHeader>
+                      <AlertDialogFooter>
+                        <AlertDialogCancel>{t("actions.cancel")}</AlertDialogCancel>
+                        <AlertDialogAction
+                          onClick={() => handleDrop(sel.courseId)}
+                        >
+                          {t("actions.drop")}
+                        </AlertDialogAction>
+                      </AlertDialogFooter>
+                    </AlertDialogContent>
+                  </AlertDialog>
                 </CardContent>
               </Card>
             ))}
@@ -130,15 +163,15 @@ export function StudentSelectionView({
 
       <section className="space-y-4">
         <div className="flex items-center justify-between">
-          <h3 className="text-lg font-semibold">Available Courses</h3>
+          <h3 className="text-lg font-semibold">{t("student.availableCourses")}</h3>
           <span className="text-sm text-muted-foreground">
-            {availableCourses.length} open
+            {availableCourses.length}
           </span>
         </div>
         {availableCourses.length === 0 ? (
           <EmptyState
-            title="No available courses"
-            description="There are no elective courses open for selection right now."
+            title={t("list.emptyStudent")}
+            description={t("description.student")}
             icon={BookOpen}
             className="h-auto border-none shadow-none"
           />
@@ -149,11 +182,11 @@ export function StudentSelectionView({
               const alreadySelected = selectedCourseIds.has(course.id)
               const isPendingThis = isPending && pendingId === course.id
               return (
-                <Card key={course.id} className="flex h-full flex-col">
+                <Card key={course.id} className="flex h-full flex-col" role="article" aria-label={course.name}>
                   <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
                     <CardTitle className="line-clamp-2 text-base">{course.name}</CardTitle>
-                    <Badge variant="outline">
-                      {ELECTIVE_STATUS_LABELS[course.status]}
+                    <Badge variant={ELECTIVE_STATUS_BADGE_VARIANTS[course.status]}>
+                      {t(ELECTIVE_STATUS_LABEL_KEYS[course.status])}
                     </Badge>
                   </CardHeader>
                   <CardContent className="flex flex-1 flex-col gap-3">
@@ -161,8 +194,8 @@ export function StudentSelectionView({
                       {course.subjectName ? (
                         <Badge variant="outline">{course.subjectName}</Badge>
                       ) : null}
-                      <span>Credit: {course.credit}</span>
-                      <span>· {SELECTION_MODE_LABELS[course.selectionMode]}</span>
+                      <span>{t("fields.credit")}: {course.credit}</span>
+                      <span>· {t(SELECTION_MODE_LABEL_KEYS[course.selectionMode])}</span>
                     </div>
                     {course.description ? (
                       <p className="line-clamp-2 text-sm text-muted-foreground">
@@ -171,27 +204,27 @@ export function StudentSelectionView({
                     ) : null}
                     <div className="grid grid-cols-2 gap-2 text-xs">
                       <div>
-                        <span className="text-muted-foreground">Teacher:</span>{" "}
+                        <span className="text-muted-foreground">{t("fields.teacher")}:</span>{" "}
                         <span className="font-medium">{course.teacherName ?? "—"}</span>
                       </div>
                       <div>
-                        <span className="text-muted-foreground">Capacity:</span>{" "}
+                        <span className="text-muted-foreground">{t("fields.capacity")}:</span>{" "}
                         <span className="font-medium">
                           {course.enrolledCount}/{course.capacity}
-                          {isFull ? " (Full)" : ""}
+                          {isFull ? ` (${t("student.capacityFull")})` : ""}
                         </span>
                       </div>
                     </div>
                     {course.schedule ? (
                       <p className="text-xs text-muted-foreground">
-                        <span className="font-medium">Schedule:</span> {course.schedule}
+                        <span className="font-medium">{t("fields.schedule")}:</span> {course.schedule}
                       </p>
                     ) : null}
                     <div className="mt-auto pt-2">
                       {alreadySelected ? (
                         <Button variant="secondary" size="sm" disabled>
                           <CheckCircle2 className="mr-1 h-3 w-3" />
-                          Already selected
+                          {t("student.selected")}
                         </Button>
                       ) : (
                         <Button
@@ -199,7 +232,7 @@ export function StudentSelectionView({
                           disabled={isPendingThis}
                           onClick={() => handleSelect(course.id)}
                         >
-                          {isPendingThis ? "Selecting..." : "Select"}
+                          {isPendingThis ? t("actions.select") + "..." : t("actions.select")}
                         </Button>
                       )}
                     </div>