fix: 修复移动端文件列表滑动问题

- 移除 touchstart 中的 event.preventDefault()，不再阻止默认滚动
- 添加 handleLongPressMove 方法检测手指移动
- 滑动超过 10px 时自动取消长按，允许正常滚动
- 为 grid 和 list 视图的文件项添加 @touchmove 事件

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Co-Authored-By: Claude <noreply@anthropic.com>

frontend/app.html

@@ -1216,7 +1216,7 @@
           
           <!-- 大图标视图 -->
           <div v-else-if="fileViewMode === 'grid'" class="file-grid">
-            <div v-for="file in files" :key="file.name" class="file-grid-item" @click="handleFileClick(file)" @contextmenu.prevent="showFileContextMenu(file, $event)" @touchstart="handleLongPressStart(file, $event)" @touchend="handleLongPressEnd">
+            <div v-for="file in files" :key="file.name" class="file-grid-item" @click="handleFileClick(file)" @contextmenu.prevent="showFileContextMenu(file, $event)" @touchstart="handleLongPressStart(file, $event)" @touchmove="handleLongPressMove($event)" @touchend="handleLongPressEnd">
               <div class="file-icon">
                 <!-- 图片缩略图 -->
                 <img v-if="file.name.match(/\.(jpg|jpeg|png|gif|bmp|svg|webp)$/i) && getThumbnailUrl(file)" 
@@ -1254,11 +1254,12 @@
                 </tr>
               </thead>
               <tbody>
-                <tr v-for="file in files" :key="file.name" 
+                <tr v-for="file in files" :key="file.name"
                     style="border-bottom: 1px solid #eee; cursor: pointer;"
                     @click="handleFileClick(file)"
                     @contextmenu.prevent="showFileContextMenu(file, $event)"
                     @touchstart="handleLongPressStart(file, $event)"
+                    @touchmove="handleLongPressMove($event)"
                     @touchend="handleLongPressEnd"
                     @mouseover="$event.currentTarget.style.background='#f9f9f9'"
                     @mouseout="$event.currentTarget.style.background='white'">