feat(PdfViewer): 添加放大缩小图标并优化缩放功能

将PDF查看器的缩放按钮从Vant组件替换为FontAwesome图标
添加faMagnifyingGlassPlus和faMagnifyingGlassMinus图标
优化双指缩放的手势处理逻辑

 <!--
  * @Date: 2025-01-21
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-10-22 12:17:03
+ * @LastEditTime: 2025-10-22 13:28:38
  * @FilePath: /mlaj/src/components/ui/PdfViewer.vue
  * @Description: PDF预览组件 - 使用pdf-vue3库
 -->
@@ -55,7 +55,8 @@
             <!-- 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-in-btn" type="default" icon="plus" round @click="zoomIn" />
+                <!-- <van-button class="zoom-btn zoom-in-btn" type="default" icon="plus" round @click="zoomIn" /> -->
+                <font-awesome-icon icon="magnifying-glass-plus" class="text-2xl text-gray-600 ml-2 mr-2" @click="zoomIn" />
                 <div class="page-jump" @click="focusPageInput">
                     <span class="page-display">{{ currentPage }}/{{ totalPages || 0 }}</span>
                     <input
@@ -70,7 +71,8 @@
                         v-show="isEditingPage"
                     />
                 </div>
-                <van-button class="zoom-btn zoom-out-btn" type="default" icon="minus" round @click="zoomOut" />
+                <!-- <van-button class="zoom-btn zoom-out-btn" type="default" icon="minus" round @click="zoomOut" /> -->
+                <font-awesome-icon icon="magnifying-glass-minus" class="text-2xl text-gray-600 ml-2 mr-2" @click="zoomOut" />
                 <van-button class="zoom-btn zoom-reset-btn" type="default" round @click="resetZoom">
                     <van-icon name="replay" size="16" />
                 </van-button>

@@ -18,10 +18,10 @@ import { library } from '@fortawesome/fontawesome-svg-core'
 /* import font awesome icon component */
 import { FontAwesomeIcon } from '@fortawesome/vue-fontawesome'
 /* import specific icons */
-import { faCirclePause, faCirclePlay, faPlay, faPause, faBackwardStep, faForwardStep, faVolumeUp, faRedo, faRepeat, faList, faChevronDown, faVolumeOff, faXmark, faFileAlt, faTimes, faEye, faFilePdf, faExternalLinkAlt, faSpinner, faExclamationCircle, faDownload, faVenus, faMars } from '@fortawesome/free-solid-svg-icons'
+import { faCirclePause, faCirclePlay, faPlay, faPause, faBackwardStep, faForwardStep, faVolumeUp, faRedo, faRepeat, faList, faChevronDown, faVolumeOff, faXmark, faFileAlt, faTimes, faEye, faFilePdf, faExternalLinkAlt, faSpinner, faExclamationCircle, faDownload, faVenus, faMars, faMagnifyingGlassPlus, faMagnifyingGlassMinus } from '@fortawesome/free-solid-svg-icons'
 
 /* add icons to the library */
-library.add(faCirclePause, faCirclePlay, faPlay, faPause, faBackwardStep, faForwardStep, faVolumeUp, faRedo, faRepeat, faList, faChevronDown, faVolumeOff, faXmark, faFileAlt, faTimes, faEye, faFilePdf, faExternalLinkAlt, faSpinner, faExclamationCircle, faDownload, faVenus, faMars )
+library.add(faCirclePause, faCirclePlay, faPlay, faPause, faBackwardStep, faForwardStep, faVolumeUp, faRedo, faRepeat, faList, faChevronDown, faVolumeOff, faXmark, faFileAlt, faTimes, faEye, faFilePdf, faExternalLinkAlt, faSpinner, faExclamationCircle, faDownload, faVenus, faMars, faMagnifyingGlassPlus, faMagnifyingGlassMinus )
 
 if (!Array.prototype.at) {
   Array.prototype.at = function(n) {