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/[id]/loading.tsx

@@ -2,7 +2,12 @@ import { Skeleton } from "@/shared/components/ui/skeleton"
 
 export default function Loading() {
   return (
-    <div className="flex h-[calc(100vh-4rem-3rem)] flex-col overflow-hidden">
+    <div
+      role="status"
+      aria-busy="true"
+      aria-label="加载中"
+      className="flex h-[calc(100vh-4rem-3rem)] flex-col overflow-hidden"
+    >
       <div className="flex items-center justify-between border-b py-3 px-6 shrink-0">
         <div className="flex items-center gap-3">
           <Skeleton className="h-6 w-48" />