feat(teacher): 题库模块（QuestionBank）

工作内容

- 新增 /teacher/questions 页面，支持 Suspense/空状态/加载态

- 题库 CRUD Server Actions：创建/更新/递归删除子题，变更后 revalidatePath

- getQuestions 支持 q/type/difficulty/knowledgePointId 筛选与分页返回 meta

- UI：表格列/筛选器/创建编辑弹窗，content JSON 兼容组卷

- 更新中文设计文档：docs/design/004_question_bank_implementation.md

src/app/(dashboard)/teacher/questions/page.tsx

@@ -1,51 +1,90 @@
 import { Suspense } from "react"
-import { Plus } from "lucide-react"
+import { ClipboardList } from "lucide-react"
 
-import { Button } from "@/shared/components/ui/button"
 import { QuestionDataTable } from "@/modules/questions/components/question-data-table"
 import { columns } from "@/modules/questions/components/question-columns"
 import { QuestionFilters } from "@/modules/questions/components/question-filters"
 import { CreateQuestionButton } from "@/modules/questions/components/create-question-button"
-import { MOCK_QUESTIONS } from "@/modules/questions/mock-data"
-import { Question } from "@/modules/questions/types"
+import { EmptyState } from "@/shared/components/ui/empty-state"
+import { Skeleton } from "@/shared/components/ui/skeleton"
+import { getQuestions } from "@/modules/questions/data-access"
+import type { QuestionType } from "@/modules/questions/types"
 
-// Simulate backend delay and filtering
-async function getQuestions(searchParams: { [key: string]: string | string[] | undefined }) {
-  // In a real app, you would call your DB or API here
-  // await new Promise((resolve) => setTimeout(resolve, 500)) // Simulate network latency
+type SearchParams = { [key: string]: string | string[] | undefined }
 
-  let filtered = [...MOCK_QUESTIONS]
+const getParam = (params: SearchParams, key: string) => {
+  const v = params[key]
+  return Array.isArray(v) ? v[0] : v
+}
 
-  const q = searchParams.q as string
-  const type = searchParams.type as string
-  const difficulty = searchParams.difficulty as string
+async function QuestionBankResults({ searchParams }: { searchParams: Promise<SearchParams> }) {
+  const params = await searchParams
 
-  if (q) {
-    filtered = filtered.filter((item) => 
-      (typeof item.content === 'string' && item.content.toLowerCase().includes(q.toLowerCase())) ||
-      (typeof item.content === 'object' && JSON.stringify(item.content).toLowerCase().includes(q.toLowerCase()))
+  const q = getParam(params, "q")
+  const type = getParam(params, "type")
+  const difficulty = getParam(params, "difficulty")
+
+  const questionType: QuestionType | undefined =
+    type === "single_choice" ||
+    type === "multiple_choice" ||
+    type === "text" ||
+    type === "judgment" ||
+    type === "composite"
+      ? type
+      : undefined
+
+  const { data: questions } = await getQuestions({
+    q: q || undefined,
+    type: questionType,
+    difficulty: difficulty && difficulty !== "all" ? Number(difficulty) : undefined,
+    pageSize: 200,
+  })
+
+  const hasFilters = Boolean(q || (type && type !== "all") || (difficulty && difficulty !== "all"))
+
+  if (questions.length === 0) {
+    return (
+      <EmptyState
+        icon={ClipboardList}
+        title={hasFilters ? "No questions match your filters" : "No questions yet"}
+        description={
+          hasFilters
+            ? "Try clearing filters or adjusting keywords."
+            : "Create your first question to start building exams and assignments."
+        }
+        action={hasFilters ? { label: "Clear filters", href: "/teacher/questions" } : undefined}
+        className="h-[360px] bg-card"
+      />
     )
   }
 
-  if (type && type !== "all") {
-    filtered = filtered.filter((item) => item.type === type)
-  }
+  return (
+    <div className="rounded-md border bg-card">
+      <QuestionDataTable columns={columns} data={questions} />
+    </div>
+  )
+}
 
-  if (difficulty && difficulty !== "all") {
-    filtered = filtered.filter((item) => item.difficulty === parseInt(difficulty))
-  }
-
-  return filtered
+function QuestionBankResultsFallback() {
+  return (
+    <div className="rounded-md border bg-card">
+      <div className="p-4">
+        <Skeleton className="h-8 w-full" />
+      </div>
+      <div className="space-y-2 p-4 pt-0">
+        {Array.from({ length: 6 }).map((_, idx) => (
+          <Skeleton key={idx} className="h-10 w-full" />
+        ))}
+      </div>
+    </div>
+  )
 }
 
 export default async function QuestionBankPage({
   searchParams,
 }: {
-  searchParams: Promise<{ [key: string]: string | string[] | undefined }>
+  searchParams: Promise<SearchParams>
 }) {
-  const params = await searchParams
-  const questions = await getQuestions(params)
-
   return (
     <div className="flex h-full flex-col space-y-8 p-8">
       <div className="flex flex-col justify-between space-y-4 md:flex-row md:items-center md:space-y-0">
@@ -62,12 +101,12 @@ export default async function QuestionBankPage({
 
       <div className="space-y-4">
         <Suspense fallback={<div className="h-10 w-full animate-pulse rounded-md bg-muted" />}>
-           <QuestionFilters />
+          <QuestionFilters />
+        </Suspense>
+
+        <Suspense fallback={<QuestionBankResultsFallback />}>
+          <QuestionBankResults searchParams={searchParams} />
         </Suspense>
-        
-        <div className="rounded-md border bg-card">
-          <QuestionDataTable columns={columns} data={questions} />
-        </div>
       </div>
     </div>
   )