feat(app): add error/loading boundaries across all dashboard routes and new routes

- Add error.tsx and loading.tsx boundaries for admin, parent, student, teacher routes

- Add admin announcements edit, audit-logs overview, curriculum-map, invitation-codes, permissions, questions, roles routes

- Add admin elective detail and components, files, course-plans, users, scheduling boundaries

- Add messages group-compose route

- Add parent course-plans, elective, grades report-card, practice routes

- Add student course-plans, elective detail, error-book dialogs, grades report-card, learning study-path, leave, schedule boundaries

- Add teacher attendance report, classes boundaries, course-plans boundaries, elective, exams analytics/edit-rich/all/create/new, grades report-card, homework boundaries, leave, lesson-plans calendar

- Add auth loading, onboarding loading, api cron

src/app/(dashboard)/student/learning/textbooks/loading.tsx

@@ -1,8 +1,14 @@
 import { Skeleton } from "@/shared/components/ui/skeleton"
+import { Card, CardContent, CardFooter, CardHeader } from "@/shared/components/ui/card"
 
 export default function Loading() {
   return (
-    <div className="space-y-8">
+    <div
+      role="status"
+      aria-busy="true"
+      aria-label="加载中"
+      className="space-y-8"
+    >
       <div className="space-y-2">
         <Skeleton className="h-8 w-40" />
         <Skeleton className="h-4 w-56" />
@@ -10,7 +16,22 @@ export default function Loading() {
       <Skeleton className="h-10 w-full max-w-md" />
       <div className="grid grid-cols-1 gap-6 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4">
         {Array.from({ length: 8 }).map((_, i) => (
-          <Skeleton key={i} className="h-48 w-full" />
+          <Card key={i} className="h-full overflow-hidden">
+            <div className="aspect-[4/3] w-full bg-muted/30 p-6 flex items-center justify-center">
+              <Skeleton className="h-24 w-20 rounded-sm" />
+            </div>
+            <CardHeader className="p-4 pb-2 space-y-2">
+              <Skeleton className="h-5 w-16" />
+              <Skeleton className="h-6 w-full" />
+            </CardHeader>
+            <CardContent className="p-4 pt-0 space-y-2">
+              <Skeleton className="h-4 w-24" />
+              <Skeleton className="h-4 w-32" />
+            </CardContent>
+            <CardFooter className="p-4 pt-0 mt-auto">
+              <Skeleton className="h-6 w-full rounded-md" />
+            </CardFooter>
+          </Card>
         ))}
       </div>
     </div>