bugfix：补全index

shudao-vue-frontend/src/views/mobile/m-Chat.vue

@@ -435,17 +435,9 @@
             <p>{{ fileError }}</p>
           </div>
           <MobilePdfViewer
-            v-else-if="previewFilePath && previewFileName.toLowerCase().endsWith('.pdf')"
+            v-else-if="previewFilePath"
             :url="previewFilePath"
           />
-          <iframe
-            v-else-if="previewFilePath"
-            :src="previewFilePath"
-            frameborder="0"
-            class="file-iframe"
-            @load="fileLoading = false"
-            @error="fileError = '文件加载失败'"
-          ></iframe>
           <div v-else class="file-empty">
             <svg class="empty-icon" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="currentColor">
               <path d="M14,2H6A2,2 0 0,0 4,4V20A2,2 0 0,0 6,22H18A2,2 0 0,0 20,20V8L14,2M18,20H6V4H13V9H18V20Z" />