fix(canvas): use icon compare toggle and move it away from prompt overlay

components/canvas/nodes/ImageNode.tsx

@@ -1660,13 +1660,30 @@ export function ImageNode({ node, isSelected }: ImageNodeProps) {
             {isSelected && !isMultiSelected && hasCompareSource && !isThisNodePicking && (
               <button
                 type="button"
-                className="absolute bottom-2 right-2 rounded-md bg-black/70 px-2 py-1 text-[11px] font-medium text-white transition-colors hover:bg-black/80"
+                className="absolute top-2 right-2 z-40 inline-flex h-8 w-8 items-center justify-center rounded-full border border-white/70 bg-black/70 text-white transition-colors hover:bg-black/80"
                 onClick={(event) => {
                   event.stopPropagation();
                   setIsCompareMode((prev) => !prev);
                 }}
+                title={isCompareMode ? "退出对比" : "开启对比"}
+                aria-label={isCompareMode ? "退出对比" : "开启对比"}
               >
-                {isCompareMode ? "退出对比" : "对比显示"}
+                {isCompareMode ? (
+                  <X className="h-4 w-4" />
+                ) : (
+                  <svg
+                    viewBox="0 0 24 24"
+                    className="h-4 w-4"
+                    fill="none"
+                    stroke="currentColor"
+                    strokeWidth="2"
+                    strokeLinecap="round"
+                    strokeLinejoin="round"
+                  >
+                    <rect x="3" y="5" width="18" height="14" rx="2" />
+                    <path d="M12 5v14" />
+                  </svg>
+                )}
               </button>
             )}
           </div>