Fix/vue nodes snap to grid (#5973)

## Summary

Enable node snap to grid in vue nodes mirroring the same behavior as
litegraph.

- Show node snap preview (semi transparent white box target behind node)
- Resize snap to grid
- Shift + drag / Auto snap 
- Multi select + group snap

## Changes

- **What**: useNodeSnap.ts useShifyKeySync.ts setups the core hooks into
both the vue node positioning/resizing system and the event forwarding
technique for communicating to litegraph.

## Review Focus

Both new composables and specifically the useNodeLayout modifications to
batch the mutations when snapping.
A key tradeoff/note is why we are using the useShifyKeySync.ts which
dispatches a new shift event to the canvas layer. This approach is the
cleaner / more declaritive method mimicking how other vue node ->
litegraph realtime events are passed.

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## Screenshots (if applicable)

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┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5973-Fix-vue-nodes-snap-to-grid-2866d73d365081c1a058d223c8c52576)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/LGraphCanvas.ts

@@ -4696,7 +4696,9 @@ export class LGraphCanvas
 
       // draw nodes
       const { visible_nodes } = this
-      const drawSnapGuides = this.#snapToGrid && this.isDragging
+      const drawSnapGuides =
+        this.#snapToGrid &&
+        (this.isDragging || layoutStore.isDraggingVueNodes.value)
 
       for (const node of visible_nodes) {
         ctx.save()
@@ -6074,7 +6076,9 @@ export class LGraphCanvas
 
     ctx.save()
     ctx.globalAlpha = 0.5 * this.editor_alpha
-    const drawSnapGuides = this.#snapToGrid && this.isDragging
+    const drawSnapGuides =
+      this.#snapToGrid &&
+      (this.isDragging || layoutStore.isDraggingVueNodes.value)
 
     for (const group of groups) {
       // out of the visible area