feat(error-book): implement error book module with SM2 spaced repetition

- Add SM2 algorithm implementation with tests for spaced repetition review scheduling

- Add data-access, schema, types, and server actions for error book CRUD

- Add components: add dialog, class overview, filters, item card, stats cards, review buttons, top wrong questions

- Add error-book routes for admin, teacher, parent, and student roles

- Add i18n messages (en, zh-CN) for error book module

src/app/(dashboard)/parent/error-book/loading.tsx

@@ -0,0 +1,18 @@
+import { Skeleton } from "@/shared/components/ui/skeleton"
+
+export default function ParentErrorBookLoading() {
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <div className="space-y-2">
+        <Skeleton className="h-8 w-[180px]" />
+        <Skeleton className="h-4 w-[280px]" />
+      </div>
+      <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-5">
+        {Array.from({ length: 5 }).map((_, idx) => (
+          <Skeleton key={idx} className="h-[120px] w-full rounded-md" />
+        ))}
+      </div>
+      <Skeleton className="h-[300px] w-full rounded-md" />
+    </div>
+  )
+}