fix: add beforeChange/afterChange to convertToSubgraph for proper undo (#7791)

## Summary
- Adds missing `beforeChange()` and `afterChange()` lifecycle calls to
`convertToSubgraph()` method

## Problem
When converting nodes to a subgraph and then pressing Ctrl+Z to undo,
the node positions were being changed from their original locations
instead of being properly restored.

## Root Cause
The `convertToSubgraph()` method in `LGraph.ts` was missing the
`beforeChange()` and `afterChange()` lifecycle calls that are needed for
proper undo/redo state tracking. These calls record the graph state
before and after modifications.

The inverse operation `unpackSubgraph()` already has these calls (see
line 1742), so this is simply matching the existing pattern.

## Solution
Add `beforeChange()` at the start of the method (after validation) and
`afterChange()` before the return.

## Testing
1. Create a workflow with several nodes positioned in specific locations
2. Select 2-3 nodes
3. Right-click → "Convert Selection to Subgraph"
4. Press Ctrl+Z to undo
5. Verify nodes return to their exact original positions

Fixes comfyanonymous/ComfyUI#11514

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7791-fix-add-beforeChange-afterChange-to-convertToSubgraph-for-proper-undo-2d86d73d36508125a2c4e4a412cced4a)
by [Unito](https://www.unito.io)

---------

Co-authored-by: RUiNtheExtinct <deepkarma001@gmail.com>

src/lib/litegraph/src/LGraph.ts

@@ -1522,6 +1522,22 @@ export class LGraph
   } {
     if (items.size === 0)
       throw new Error('Cannot convert to subgraph: nothing to convert')
+
+    // Record state before conversion for proper undo support
+    this.beforeChange()
+
+    try {
+      return this._convertToSubgraphImpl(items)
+    } finally {
+      // Mark state change complete for proper undo support
+      this.afterChange()
+    }
+  }
+
+  private _convertToSubgraphImpl(items: Set<Positionable>): {
+    subgraph: Subgraph
+    node: SubgraphNode
+  } {
     const { state, revision, config } = this
     const firstChild = [...items][0]
     if (items.size === 1 && firstChild instanceof LGraphGroup) {
@@ -1728,6 +1744,7 @@ export class LGraph
 
     subgraphNode._setConcreteSlots()
     subgraphNode.arrange()
+
     this.canvasAction((c) =>
       c.canvas.dispatchEvent(
         new CustomEvent('subgraph-converted', {
@@ -1746,9 +1763,23 @@ export class LGraph
     if (!(subgraphNode instanceof SubgraphNode))
       throw new Error('Can only unpack Subgraph Nodes')
 
+    // Record state before unpacking for proper undo support
+    this.beforeChange()
+
+    try {
+      this._unpackSubgraphImpl(subgraphNode, options)
+    } finally {
+      // Mark state change complete for proper undo support
+      this.afterChange()
+    }
+  }
+
+  private _unpackSubgraphImpl(
+    subgraphNode: SubgraphNode,
+    options?: { skipMissingNodes?: boolean }
+  ) {
     const skipMissingNodes = options?.skipMissingNodes ?? false
 
-    this.beforeChange()
     //NOTE: Create bounds can not be called on positionables directly as the subgraph is not being displayed and boundingRect is not initialized.
     //NOTE: NODE_TITLE_HEIGHT is explicitly excluded here
     const positionables = [
@@ -2019,7 +2050,6 @@ export class LGraph
     }
 
     this.canvasAction((c) => c.selectItems(toSelect))
-    this.afterChange()
   }
 
   /**