feat(LivePreviewEditor): 为目录侧边栏添加宽度拖拽调整功能

添加目录侧边栏的宽度拖拽调整支持，提升用户自定义布局的灵活性。
- 新增拖拽手柄组件，用户可调整侧边栏宽度（150px-600px范围）
- 拖拽时提供视觉反馈（光标变化、手柄高亮）
- 移除侧边栏固定宽度样式，改为JS动态控制
- 拖拽期间禁用过渡动画以避免视觉延迟

src/components/LivePreviewEditor.vue

@@ -4,8 +4,12 @@
     
     <div class="editor-main">
       <!-- 目录大纲侧边栏 -->
-      <div class="toc-sidebar" :class="{ collapsed: !showToc }">
-        <div class="toc-content">
+      <div 
+        class="toc-sidebar" 
+        :class="{ collapsed: !showToc, resizing: isResizing }"
+        :style="{ width: showToc ? `${tocWidth}px` : '0px' }"
+      >
+        <div class="toc-content" :style="{ width: `${tocWidth}px` }">
           <div v-if="toc.length === 0" class="toc-empty">暂无大纲</div>
           <div 
             v-for="(item, index) in toc" 
@@ -20,6 +24,13 @@
         </div>
       </div>
       
+      <!-- 拖拽手柄 -->
+      <div 
+        v-if="showToc" 
+        class="toc-resizer" 
+        @mousedown.prevent="startResize"
+      ></div>
+
       <codemirror 
         v-model="code" 
         placeholder="请输入 Markdown 内容..." 
@@ -84,6 +95,36 @@ const { applyHeading, wrapSelection, prefixLines, insertLink } = useMarkdownActi
 // 目录相关
 const showToc = ref(true);
 const toc = shallowRef([]);
+const tocWidth = ref(220);
+const isResizing = ref(false);
+let startX = 0;
+let startWidth = 0;
+
+const startResize = (e) => {
+  isResizing.value = true;
+  startX = e.clientX;
+  startWidth = tocWidth.value;
+  
+  document.addEventListener('mousemove', handleResize);
+  document.addEventListener('mouseup', stopResize);
+  document.body.style.cursor = 'col-resize';
+  document.body.style.userSelect = 'none';
+};
+
+const handleResize = (e) => {
+  if (!isResizing.value) return;
+  const diff = e.clientX - startX;
+  const newWidth = Math.max(150, Math.min(600, startWidth + diff));
+  tocWidth.value = newWidth;
+};
+
+const stopResize = () => {
+  isResizing.value = false;
+  document.removeEventListener('mousemove', handleResize);
+  document.removeEventListener('mouseup', stopResize);
+  document.body.style.cursor = '';
+  document.body.style.userSelect = '';
+};
 
 const debounce = (fn, delay) => {
   let timer = null;
@@ -480,16 +521,20 @@ onUnmounted(() => {
 }
 
 .toc-sidebar {
-  width: 220px;
+  /* width: 220px;  由 JS 控制 */
   flex-shrink: 0;
   border-right: 1px solid var(--border-color);
   overflow-y: auto;
   overflow-x: hidden;
   background-color: var(--card-background);
-  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
+  transition: width 0.3s cubic-bezier(0.4, 0, 0.2, 1), opacity 0.3s;
   opacity: 1;
 }
 
+.toc-sidebar.resizing {
+  transition: none;
+}
+
 .toc-sidebar.collapsed {
   width: 0;
   opacity: 0;
@@ -497,10 +542,25 @@ onUnmounted(() => {
 }
 
 .toc-content {
-  width: 220px; /* 固定宽度，防止内容挤压 */
+  /* width: 220px; 由 JS 控制 */
   padding: 12px 0;
 }
 
+.toc-resizer {
+  width: 4px;
+  cursor: col-resize;
+  background-color: transparent;
+  transition: background-color 0.2s;
+  flex-shrink: 0;
+  margin-left: -1px; /* 重叠边框 */
+  z-index: 10;
+  position: relative;
+}
+
+.toc-resizer:hover, .toc-sidebar.resizing + .toc-resizer {
+  background-color: var(--primary-color);
+}
+
 .toc-empty {
   padding: 20px;
   text-align: center;