feat(markdown): 只读内容支持 Markdown 渲染

- 新增 MarkdownRenderer.vue 组件，基于 marked 解析 GFM
- 学习残片/报告历史列表：纯文本 {{ }} 替换为 MarkdownRenderer
- ReviewDetail.vue content-body：p 标签逐行渲染替换为 MarkdownRenderer
- 结束会话总结框：增加「编辑/预览」切换，预览模式实时渲染 markdown
- 学习预期展示也改为 MarkdownRenderer

src/components/StartTask.vue

@@ -13,6 +13,7 @@ import { useStudyFragment } from "@/components/composables/fragment";
 import { getFragmentsBySession, updateFragments } from "@/api/reportFragments";
 import { getExpectation, getReportDraft, getTaskFragments, getTaskReports, upsertExpectation } from "@/api/studySessions";
 import router from "@/router";
+import MarkdownRenderer from "@/components/MarkdownRenderer.vue";
 
 const {
   fragmentsDialogVisible,
@@ -24,6 +25,7 @@ const {
 
 const summaryDialogVisible = ref(false);
 const summaryContent = ref("");
+const summaryPreview = ref(false);
 const summaryLoading = ref(false);
 const summaryLoadingSeconds = ref(0);
 let summaryLoadingTimer: ReturnType<typeof setInterval> | null = null;
@@ -666,7 +668,7 @@ onUnmounted(() => {
             <div v-loading="loadingHistory" class="history-list">
               <div v-for="item in historyFragments" :key="item.id" class="history-item">
                 <span class="session-tag">{{ item.sessionNum }}</span>
-                <span class="history-content">{{ item.content }}</span>
+                <MarkdownRenderer :content="item.content" />
               </div>
               <el-empty v-if="!loadingHistory && historyFragments.length === 0" description="暂未找到匹配的残片" :image-size="48"></el-empty>
             </div>
@@ -676,7 +678,7 @@ onUnmounted(() => {
             <div v-loading="loadingHistory" class="history-list">
               <div v-for="item in historyReports" :key="item.id" class="history-item report-item">
                 <span class="session-tag">{{ item.sessionNum }}</span>
-                <p class="history-content">{{ item.content }}</p>
+                <MarkdownRenderer :content="item.content" />
               </div>
               <el-empty v-if="!loadingHistory && historyReports.length === 0" description="暂未找到匹配的报告" :image-size="48" />
             </div>
@@ -721,21 +723,39 @@ onUnmounted(() => {
     </template>
   </el-dialog>
 
-  <el-dialog v-model="summaryDialogVisible" title="结束会话总结" width="560px">
+  <el-dialog v-model="summaryDialogVisible" title="结束会话总结" width="640px">
     <div v-if="expectationSaved" class="summary-expectation">
       <span class="expectation-label">本次预期</span>
-      <span>{{ expectationSaved }}</span>
+      <MarkdownRenderer :content="expectationSaved" />
     </div>
     <p v-if="summaryLoading" class="ai-waiting">
       AI 正在聚合残片生成草稿，已等待 {{ summaryLoadingSeconds }} 秒…
     </p>
-    <el-input
-      v-loading="summaryLoading"
-      type="textarea"
-      v-model="summaryContent"
-      placeholder="总结本次学到的内容（已有残片时自动生成草稿，可修改）"
-      :rows="8"
-    />
+    <div class="summary-editor">
+      <div class="summary-toolbar">
+        <el-button
+          size="small"
+          :type="summaryPreview ? '' : 'primary'"
+          @click="summaryPreview = false"
+        >编辑</el-button>
+        <el-button
+          size="small"
+          :type="summaryPreview ? 'primary' : ''"
+          @click="summaryPreview = true"
+        >预览</el-button>
+      </div>
+      <el-input
+        v-if="!summaryPreview"
+        v-loading="summaryLoading"
+        type="textarea"
+        v-model="summaryContent"
+        placeholder="总结本次学到的内容（已有残片时自动生成草稿，可修改）"
+        :rows="8"
+      />
+      <div v-else class="summary-preview">
+        <MarkdownRenderer :content="summaryContent" />
+      </div>
+    </div>
     <template #footer>
       <el-button @click="closeSummaryDialog">取消</el-button>
       <el-button type="success" @click="endTimer(summaryContent)">确认结束</el-button>
@@ -819,6 +839,33 @@ onUnmounted(() => {
   color: var(--text-secondary);
 }
 
+.summary-editor {
+  border: 1px solid #e0e8e0;
+  border-radius: 6px;
+  overflow: hidden;
+}
+
+.summary-toolbar {
+  display: flex;
+  gap: 0;
+  border-bottom: 1px solid #e0e8e0;
+  background: #f9fbf9;
+  padding: 4px;
+}
+
+.summary-toolbar .el-button {
+  border-radius: 4px;
+  border: none;
+}
+
+.summary-preview {
+  padding: 12px 16px;
+  min-height: 200px;
+  max-height: 360px;
+  overflow-y: auto;
+  background: #fff;
+}
+
 .status-text {
   font-size: 14px;
   color: var(--text-secondary);