fix: emit layout change for batch node bounds (#5939)

## Summary

Fixes issue where node size changes are not serialized by routing
DOM-driven node bounds updates through a single CRDT operation so Vue
node geometry stays synchronized with LiteGraph.

## Changes

- **What**: Added `BatchUpdateBoundsOperation` to the layout store,
applied it via the existing Yjs pipeline, notified link sync to
recompute touched nodes, and covered the path with a regression test

## Review Focus

Correctness of the new batch operation when multiple nodes update
simultaneously, especially remote replay/undo scenarios and link
geometry recomputation.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5939-fix-emit-layout-change-for-batch-node-bounds-2846d73d365081db8f8cca5bf7b85308)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

src/renderer/core/spatial/SpatialIndex.ts

@@ -55,6 +55,17 @@ export class SpatialIndexManager {
     this.invalidateCache()
   }
 
+  /**
+   * Batch update multiple nodes' bounds in the spatial index
+   * More efficient than calling update() multiple times as it only invalidates cache once
+   */
+  batchUpdate(updates: Array<{ nodeId: NodeId; bounds: Bounds }>): void {
+    for (const { nodeId, bounds } of updates) {
+      this.quadTree.update(nodeId, bounds)
+    }
+    this.invalidateCache()
+  }
+
   /**
    * Remove a node from the spatial index
    */