窗口失焦时丢弃未提交的树拖拽

PreviewWorkspace.tsx 的 onWindowBlur 一并清掉 treeDragRef 与树拖拽预览偏移：失焦时浏览器不一定补 pointercancel，陈旧手势会被后续 pointerup 复用并把意外偏移写进文档
tests/previewRightPanDrag.test.tsx 补失焦后抬起不提交偏移的用例

apps/ai-game-creator-shell/src/view/ui-editor/components/preview/PreviewWorkspace.tsx

@@ -404,6 +404,17 @@ export function PreviewWorkspace({
       rightPressSequenceRef.current = false;
       rightPanRef.current = null;
       setIsPanning(false);
+      // 失焦时浏览器不一定补 pointercancel：丢掉未提交的树拖拽，避免后续指针事件
+      // 复用陈旧手势把意外偏移写进文档。
+      const drag = treeDragRef.current;
+      if (drag) {
+        treeDragRef.current = null;
+        setPreviewTreeOffsets((current) => {
+          const next = new Map(current);
+          next.delete(drag.treeId);
+          return next;
+        });
+      }
     };
     window.addEventListener('keydown', onKeyDown);
     window.addEventListener('keyup', onKeyUp);