改进 Minimap 组件的 ref 赋值逻辑，支持回调函数和 ref 对象两种形式

packages/image-canvas-react/src/Minimap.tsx

@@ -18,9 +18,17 @@ export function Minimap({
   stageClassName?: string;
   viewportClassName?: string;
 }) {
+  const assignMinimapRef = (element: HTMLButtonElement | null) => {
+    if (typeof minimapRef === 'function') {
+      minimapRef(element);
+    } else if (minimapRef) {
+      minimapRef.current = element;
+    }
+  };
+
   return (
     <button
-      ref={minimapRef}
+      ref={assignMinimapRef}
       type="button"
       className={`genarrative-image-canvas__minimap ${className}`.trim()}
       aria-label="画布小地图"