refactor(ui): 优化用户界面和代码显示

- 将"清空"按钮文本改为"返回"，提高用户友好性
- 优化代码预览显示，移除代码块内部滚动条，提高可读性

biji-qianduan/src/components/HomePage.vue

@@ -39,7 +39,7 @@
               <el-icon class="edit-icon" @click="openRenameDialog(selectedFile, 'file')"><Edit /></el-icon>
             </h2>
             <div class="actions">
-              <el-button v-if="!showEditor" type="primary" @click="selectedFile = null">清空</el-button>
+              <el-button v-if="!showEditor" type="primary" @click="selectedFile = null">返回</el-button>
               <el-button v-if="!showEditor && userStore.isLoggedIn" type="primary" @click="editNote(selectedFile); isCollapsed = true">编辑</el-button>
               <el-button v-if="!showEditor && userStore.isLoggedIn" type="danger" @click="deleteNote(selectedFile)">删除</el-button>
               <el-button v-if="showEditor" type="primary" @click="showEditor = !showEditor; previewFile(editData)">返回</el-button>
@@ -731,6 +731,20 @@ const handleExportMd = () => {
 .dark-theme .vditor-toolbar__item--current {
   background-color: var(--primary-color-light) !important;
 }
+
+/* 移除预览中代码块的内部滚动条 */
+.markdown-preview .vditor-reset pre {
+  max-height: none !important;
+  overflow: visible !important;
+}
+
+.markdown-preview .vditor-reset pre code {
+  max-height: none !important;
+  overflow-y: visible !important;
+  word-break: break-all !important;
+  white-space: pre-wrap !important;
+  display: block;
+}
 </style>
 
 <style scoped>