feat: 顶部工具栏新增叠加图片按钮

index.html

@@ -11,6 +11,7 @@
         <!-- 顶部工具栏 -->
         <div class="toolbar">
             <button class="btn" id="addImageBtn">添加图片</button>
+            <button class="btn" id="addOverlayBtn">层叠图</button>
             <button class="btn btn-primary" id="saveBtn">保存/预览</button>
         </div>
 
@@ -53,6 +54,8 @@
                 <div class="preview-bg-layer" id="bgLayer">
                     <img id="bgImage" src="" alt="背景图">
                 </div>
+                <!-- 层叠图图层 -->
+                <div class="overlay-layer" id="overlayLayer"></div>
                 <!-- 拖拽辅助线 -->
                 <div class="guide-line guide-horizontal" id="guideH"></div>
                 <div class="guide-line guide-vertical" id="guideV"></div>