feat(app): add error/loading boundaries and update dashboard routes

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

- Add dashboard-error-fallback and dashboard-loading-skeleton components

- Add student/learning page, parent/leave routes, teacher textbook components

- Update existing app routes across auth, dashboard, and API endpoints

- Update proxy middleware and next-auth type declarations

src/app/(dashboard)/management/grade/classes/error.tsx

@@ -0,0 +1,27 @@
+"use client"
+
+import { AlertCircle } from "lucide-react"
+
+import { EmptyState } from "@/shared/components/ui/empty-state"
+
+export default function ManagementGradeClassesError({
+  reset,
+}: {
+  error: Error & { digest?: string }
+  reset: () => void
+}) {
+  return (
+    <div className="flex h-full flex-col items-center justify-center space-y-4 p-8">
+      <EmptyState
+        icon={AlertCircle}
+        title="年级班级页面加载失败"
+        description="抱歉，页面加载时发生了意外错误。请稍后重试。"
+        action={{
+          label: "重试",
+          onClick: () => reset(),
+        }}
+        className="border-none shadow-none h-auto"
+      />
+    </div>
+  )
+}

src/app/(dashboard)/management/grade/classes/loading.tsx

@@ -0,0 +1,24 @@
+import { Card, CardContent, CardHeader } from "@/shared/components/ui/card"
+import { Skeleton } from "@/shared/components/ui/skeleton"
+
+export default function ManagementGradeClassesLoading() {
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <div className="space-y-2">
+        <Skeleton className="h-8 w-48" />
+        <Skeleton className="h-4 w-64" />
+      </div>
+
+      <Card>
+        <CardHeader>
+          <Skeleton className="h-5 w-32" />
+        </CardHeader>
+        <CardContent className="space-y-3">
+          {Array.from({ length: 6 }).map((_, i) => (
+            <Skeleton key={i} className="h-12 w-full" />
+          ))}
+        </CardContent>
+      </Card>
+    </div>
+  )
+}