fix(exams): use slice to preserve full content when wrapping selections

Root cause: wrapIn (Tiptap's built-in command) can fail or lose content
when the selection spans multiple paragraphs or partial paragraphs. When
users selected a long reading passage and clicked "复合" (composite),
the content was destroyed — only fragments remained.

Fix: replace wrapIn with a manual slice-based approach:
1. Use doc.slice(from, to) to get the complete node structure of the
   selection (preserves paragraphs, lists, images, etc.)
2. deleteRange to remove the original selection
3. insertContentAt to insert a new questionBlock/groupBlock/sectionBlock
   containing the sliced content

This is more reliable than wrapIn because it doesn't depend on
ProseMirror's wrapping logic, which has edge cases with multi-paragraph
selections. The slice API captures the exact node structure, so no
content is lost.

Applied to all three wrapping operations:
- insertQuestion (questionBlock)
- insertGroup (groupBlock)
- insertSection (sectionBlock)

src/modules/exams/editor/selection-toolbar.tsx

@@ -151,43 +151,40 @@ export function SelectionToolbar({
   const insertQuestion = (type: QuestionBlockType) => {
     const score = type === "composite" ? 5 : 2
     if (hasTextSelection) {
-      // 先尝试 wrapIn(普通情况下可用)
-      const wrapped = editor.commands.wrapInQuestion({ type, score })
-      if (!wrapped) {
-        // wrapIn 失败(通常在 isolating 节点如复合题块内):
-        // 获取选中文本,删除选区,插入包含选中文本的 questionBlock
-        // 这样不会清空内容,而是把选中文本转为新的子题
+      // 用 slice 获取选区内的完整节点结构(保留段落/列表/图片等),
+      // 然后用 questionBlock 包裹这些内容。这比 wrapIn 更可靠,
+      // 因为 wrapIn 在选区跨越多个段落或部分段落时可能失败或丢失内容。
       const { from, to } = editor.state.selection
-        const selectedText = editor.state.doc.textBetween(from, to, "\n")
-        const lines = selectedText
-          .split("\n")
-          .filter((l) => l.trim().length > 0)
-        const content = lines.length > 0
-          ? lines.map((line) => ({
-              type: "paragraph",
-              content: [{ type: "text", text: line }],
-            }))
+      const slice = editor.state.doc.slice(from, to)
+      const sliceContent = slice.content.toJSON
+        ? (slice.content.toJSON() as unknown[])
+        : Array.isArray(slice.content.content)
+          ? slice.content.content.map((n) => n.toJSON())
+          : []
+
+      // 确保 content: "block+" 满足(非空)
+      const validContent =
+        sliceContent.length > 0
+          ? sliceContent
           : [{ type: "paragraph", content: [{ type: "text", text: " " }] }]
 
       editor.chain()
         .focus()
-          .deleteSelection()
-          .insertContent({
+        .deleteRange({ from, to })
+        .insertContentAt(from, {
           type: "questionBlock",
           attrs: { type, score, questionId: "" },
-            content,
+          content: validContent,
         })
         .run()
-      }
     } else {
       // 未选中文本时:插入空题目块
       editor.chain().focus().insertQuestion({ type, score }).run()
     }
   }
 
-  /** 通用降级包裹:wrapIn 失败时,把选中文本转为指定节点 */
-  const wrapOrInsert = (
-    wrapFn: () => boolean,
+  /** 通用包裹:用 slice 获取选区完整节点结构,包裹到指定节点中 */
+  const wrapSelection = (
     insertFn: () => void,
     nodeType: "groupBlock" | "sectionBlock",
     attrs: Record<string, unknown>,
@@ -197,34 +194,33 @@ export function SelectionToolbar({
       insertFn()
       return
     }
-    const wrapped = wrapFn()
-    if (!wrapped) {
-      // wrapIn 失败:获取选中文本,删除选区,插入包含选中文本的节点
+    // 用 slice 获取选区内的完整节点结构,确保不丢失内容
     const { from, to } = editor.state.selection
-      const selectedText = editor.state.doc.textBetween(from, to, "\n")
-      const lines = selectedText.split("\n").filter((l) => l.trim().length > 0)
-      const content = lines.length > 0
-        ? lines.map((line) => ({
-            type: "paragraph",
-            content: [{ type: "text", text: line }],
-          }))
+    const slice = editor.state.doc.slice(from, to)
+    const sliceContent = slice.content.toJSON
+      ? (slice.content.toJSON() as unknown[])
+      : Array.isArray(slice.content.content)
+        ? slice.content.content.map((n) => n.toJSON())
+        : []
+
+    const validContent =
+      sliceContent.length > 0
+        ? sliceContent
         : [{ type: "paragraph", content: [{ type: "text", text: " " }] }]
 
     editor.chain()
       .focus()
-        .deleteSelection()
-        .insertContent({
+      .deleteRange({ from, to })
+      .insertContentAt(from, {
         type: nodeType,
         attrs: { ...attrs, title: defaultTitle },
-          content,
+        content: validContent,
       })
       .run()
   }
-  }
 
   const insertGroup = () => {
-    wrapOrInsert(
-      () => editor.commands.wrapInGroup("一、选择题", ""),
+    wrapSelection(
       () => editor.chain().focus().insertGroup("一、选择题", "").run(),
       "groupBlock",
       { instruction: "" },
@@ -233,8 +229,7 @@ export function SelectionToolbar({
   }
 
   const insertSection = () => {
-    wrapOrInsert(
-      () => editor.commands.wrapInSection("第Ⅰ卷 选择题", 1),
+    wrapSelection(
       () => editor.chain().focus().insertSection("第Ⅰ卷 选择题", 1).run(),
       "sectionBlock",
       { level: 1 },