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)/teacher/homework/loading.tsx

@@ -0,0 +1,17 @@
+import { Skeleton } from "@/shared/components/ui/skeleton"
+
+/**
+ * teacher/homework/loading.tsx
+ * 作业模块入口骨架屏（实际会重定向到 /assignments，但保留骨架屏以避免空白闪烁）。
+ */
+export default function Loading() {
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <div className="space-y-2">
+        <Skeleton className="h-7 w-48" />
+        <Skeleton className="h-4 w-72" />
+      </div>
+      <Skeleton className="h-96 w-full" />
+    </div>
+  )
+}