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/modules/questions/components/question-columns.tsx

@@ -5,34 +5,38 @@ import { ColumnDef } from "@tanstack/react-table"
 import { Badge } from "@/shared/components/ui/badge"
 import { Checkbox } from "@/shared/components/ui/checkbox"
 import { Question, QuestionType } from "../types"
-import { cn } from "@/shared/lib/utils"
 import { QuestionActions } from "./question-actions"
 
-// Helper for Type Colors
 const getTypeColor = (type: QuestionType) => {
   switch (type) {
     case "single_choice":
-      return "default"; // Primary
+      return "default"
     case "multiple_choice":
-      return "secondary";
+      return "secondary"
     case "judgment":
-      return "outline";
+      return "outline"
     case "text":
-      return "secondary"; // Changed from 'accent' which might not be a valid badge variant key in standard shadcn, usually it's default, secondary, destructive, outline.
+      return "secondary"
     default:
-      return "secondary";
+      return "secondary"
   }
 }
 
 const getTypeLabel = (type: QuestionType) => {
-    switch (type) {
-      case "single_choice": return "Single Choice";
-      case "multiple_choice": return "Multiple Choice";
-      case "judgment": return "True/False";
-      case "text": return "Short Answer";
-      case "composite": return "Composite";
-      default: return type;
-    }
+  switch (type) {
+    case "single_choice":
+      return "Single Choice"
+    case "multiple_choice":
+      return "Multiple Choice"
+    case "judgment":
+      return "True/False"
+    case "text":
+      return "Short Answer"
+    case "composite":
+      return "Composite"
+    default:
+      return type
+  }
 }
 
 export const columns: ColumnDef<Question>[] = [
@@ -71,14 +75,20 @@ export const columns: ColumnDef<Question>[] = [
     accessorKey: "content",
     header: "Content",
     cell: ({ row }) => {
-      const content = row.getValue("content");
-      let preview = "";
-      if (typeof content === 'string') {
-        preview = content;
-      } else if (content && typeof content === 'object') {
-         preview = JSON.stringify(content).slice(0, 50);
+      const content = row.getValue("content") as unknown
+      let preview = ""
+      if (typeof content === "string") {
+        preview = content
+      } else if (content && typeof content === "object") {
+        const text = (content as { text?: unknown }).text
+        if (typeof text === "string") {
+          preview = text
+        } else {
+          preview = JSON.stringify(content)
+        }
       }
-      
+      preview = preview.slice(0, 80)
+
       return (
         <div className="max-w-[400px] truncate font-medium" title={preview}>
           {preview}
@@ -90,17 +100,23 @@ export const columns: ColumnDef<Question>[] = [
     accessorKey: "difficulty",
     header: "Difficulty",
     cell: ({ row }) => {
-      const diff = row.getValue("difficulty") as number;
-      // 1-5 scale
+      const diff = row.getValue("difficulty") as number
+      const label =
+        diff === 1
+          ? "Easy"
+          : diff === 2
+            ? "Easy-Med"
+            : diff === 3
+              ? "Medium"
+              : diff === 4
+                ? "Med-Hard"
+                : "Hard"
       return (
-        <div className="flex items-center">
-            <span className={cn("font-medium", 
-                diff <= 2 ? "text-green-600" : 
-                diff === 3 ? "text-yellow-600" : "text-red-600"
-            )}>
-                {diff === 1 ? "Easy" : diff === 2 ? "Easy-Med" : diff === 3 ? "Medium" : diff === 4 ? "Med-Hard" : "Hard"}
-            </span>
-            <span className="ml-1 text-xs text-muted-foreground">({diff})</span>
+        <div className="flex items-center gap-2">
+          <Badge variant="outline" className="tabular-nums">
+            {label}
+          </Badge>
+          <span className="text-xs text-muted-foreground tabular-nums">({diff})</span>
         </div>
       )
     },
@@ -109,22 +125,24 @@ export const columns: ColumnDef<Question>[] = [
     accessorKey: "knowledgePoints",
     header: "Knowledge Points",
     cell: ({ row }) => {
-        const kps = row.original.knowledgePoints;
-        if (!kps || kps.length === 0) return <span className="text-muted-foreground">-</span>;
-        
-        return (
-            <div className="flex flex-wrap gap-1">
-                {kps.slice(0, 2).map(kp => (
-                    <Badge key={kp.id} variant="outline" className="text-xs">
-                        {kp.name}
-                    </Badge>
-                ))}
-                {kps.length > 2 && (
-                    <Badge variant="outline" className="text-xs">+{kps.length - 2}</Badge>
-                )}
-            </div>
-        )
-    }
+      const kps = row.original.knowledgePoints
+      if (!kps || kps.length === 0) return <span className="text-muted-foreground">-</span>
+
+      return (
+        <div className="flex flex-wrap gap-1">
+          {kps.slice(0, 2).map((kp) => (
+            <Badge key={kp.id} variant="outline" className="text-xs">
+              {kp.name}
+            </Badge>
+          ))}
+          {kps.length > 2 && (
+            <Badge variant="outline" className="text-xs">
+              +{kps.length - 2}
+            </Badge>
+          )}
+        </div>
+      )
+    },
   },
   {
     accessorKey: "createdAt",
@@ -132,7 +150,7 @@ export const columns: ColumnDef<Question>[] = [
     cell: ({ row }) => {
       return (
         <span className="text-muted-foreground text-xs whitespace-nowrap">
-            {new Date(row.getValue("createdAt")).toLocaleDateString()}
+          {new Date(row.getValue("createdAt")).toLocaleDateString()}
         </span>
       )
     },