refactor(PdfViewer): 将关闭按钮移至缩放控制栏并调整样式

将顶部关闭按钮移除，功能迁移至缩放控制栏，同时调整按钮位置样式以改善用户体验

 <!--
  * @Date: 2025-01-21
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-10-22 10:49:55
+ * @LastEditTime: 2025-10-22 11:21:20
  * @FilePath: /mlaj/src/components/ui/PdfViewer.vue
  * @Description: PDF预览组件 - 使用pdf-vue3库
 -->
@@ -50,11 +50,11 @@
                 </div>
             </div>
 
-            <!-- 关闭按钮 -->
-            <van-button class="close-btn" type="default" icon="cross" round @click="handleClose" />
+            <!-- 已移除顶部关闭按钮，关闭功能迁移至控制栏 -->
 
             <!-- 缩放控制按钮 -->
             <div v-if="!loading && !loadingError" class="zoom-controls">
+                <van-button class="zoom-btn zoom-close-btn" type="default" icon="cross" round @click="handleClose" />
                 <van-button class="zoom-btn zoom-out-btn" type="default" icon="minus" round @click="zoomOut" />
                 <div class="zoom-level">{{ Math.round(zoomLevel * 100) }}%</div>
                 <van-button class="zoom-btn zoom-in-btn" type="default" icon="plus" round @click="zoomIn" />
@@ -540,8 +540,8 @@ const addPreventSaveListeners = () => {
 /* 关闭按钮样式 */
 .close-btn {
     position: fixed;
-    right: 20px;
-    top: 20px;
+    left: 20px;
+    bottom: 40px;
     z-index: 100;
     width: 40px;
     height: 40px;
@@ -554,7 +554,7 @@ const addPreventSaveListeners = () => {
 /* 缩放控制按钮样式 */
 .zoom-controls {
     position: fixed;
-    bottom: 30px;
+    bottom: 60px;
     left: 50%;
     transform: translateX(-50%);
     z-index: 100;