fix: fix image upload in canvas ImageNode

Added stopPropagation to prevent Rnd click handler from intercepting the file input click event. Added an explicit button for better UX.

components/canvas/nodes/ImageNode.tsx

@@ -178,16 +178,24 @@ export function ImageNode({ node, isSelected }: ImageNodeProps) {
             <span className="text-sm text-destructive">生成失败</span>
           </div>
         ) : (
-          <label className="w-full h-full flex flex-col items-center justify-center bg-muted cursor-pointer hover:bg-muted/80 transition-colors">
+          <div className="w-full h-full flex flex-col items-center justify-center bg-muted">
             <ImagePlus className="h-8 w-8 text-muted-foreground mb-2" />
-            <span className="text-sm text-muted-foreground">点击上传图片</span>
-            <input
-              type="file"
-              accept="image/*"
-              className="hidden"
-              onChange={handleImageUpload}
-            />
-          </label>
+            <span className="text-sm text-muted-foreground mb-3">点击上传图片</span>
+            <label 
+              className="cursor-pointer"
+              onClick={(e) => e.stopPropagation()}
+            >
+              <input
+                type="file"
+                accept="image/*"
+                className="hidden"
+                onChange={handleImageUpload}
+              />
+              <span className="px-4 py-2 bg-primary text-primary-foreground text-sm rounded-md hover:bg-primary/90 transition-colors">
+                选择文件
+              </span>
+            </label>
+          </div>
         )}
 
         {/* 处理中遮罩 */}