fix: Prune invalid builder mappings on load (#9376)

## Summary

- extract resolveNode to reusable util
- remove mid builder pruning
- handle missing widgets with label

## Review Focus

`resolveNode` was simplified for subgraphs by calling getNodeById on
each of the subgraphs instead of searching their inner nodes manually.

## Screenshots (if applicable)

"Widget not visible"
<img width="657" height="822" alt="image"
src="https://github.com/user-attachments/assets/ab7d1e87-3210-4e54-876a-07881974b5c7"
/>
<img width="674" height="375" alt="image"
src="https://github.com/user-attachments/assets/c50ec871-d423-43d6-8e1e-7b1a362f621c"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9376-fix-Prune-invalid-builder-mappings-on-load-3196d73d3650811280c2d459ed0271af)
by [Unito](https://www.unito.io)

src/utils/litegraphUtil.ts

@@ -20,8 +20,10 @@ import type {
   IComboWidget,
   WidgetCallbackOptions
 } from '@/lib/litegraph/src/types/widgets'
+import type { NodeId } from '@/lib/litegraph/src/LGraphNode'
 import type { InputSpec } from '@/schemas/nodeDef/nodeDefSchemaV2'
 import { useToastStore } from '@/platform/updates/common/toastStore'
+import { app } from '@/scripts/app'
 import { t } from '@/i18n'
 
 type ImageNode = LGraphNode & { imgs: HTMLImageElement[] | undefined }
@@ -304,6 +306,20 @@ export function getLinkTypeColor(typeName: string): string {
   return LGraphCanvas.link_type_colors[typeName] ?? LiteGraph.LINK_COLOR
 }
 
+export function resolveNode(
+  nodeId: NodeId,
+  graph: LGraph | null | undefined = app.rootGraph
+): LGraphNode | undefined {
+  if (!graph) return undefined
+  const found = graph.getNodeById(nodeId)
+  if (found) return found
+  for (const sg of graph.subgraphs.values()) {
+    const node = sg.getNodeById(nodeId)
+    if (node) return node
+  }
+  return undefined
+}
+
 export function isLoad3dNode(node: LGraphNode) {
   return (
     node &&