[bugfix] Fix TypeScript errors in SubgraphNode type checking

Add proper type validation for subgraph node selection before calling
SubgraphNode-specific methods. This prevents undefined values from being
passed to functions expecting SubgraphNode parameters.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/composables/useCoreCommands.ts

@@ -10,7 +10,8 @@ import {
   LGraphEventMode,
   LGraphGroup,
   LGraphNode,
-  LiteGraph
+  LiteGraph,
+  SubgraphNode
 } from '@/lib/litegraph/src/litegraph'
 import { Point } from '@/lib/litegraph/src/litegraph'
 import { api } from '@/scripts/api'
@@ -823,6 +824,7 @@ export function useCoreCommands(): ComfyCommand[] {
         if (!graph) throw new TypeError('Canvas has no graph or subgraph set.')
 
         const subgraphNode = app.canvas.selectedItems.values().next().value
+        if (!(subgraphNode instanceof SubgraphNode)) return
         useNodeOutputStore().revokeSubgraphPreviews(subgraphNode)
         graph.unpackSubgraph(subgraphNode)
       }