fix: stabilize nested subgraph promoted widget resolution (#9282)

## Summary

Fix multiple issues with promoted widget resolution in nested subgraphs,
ensuring correct value propagation, slot matching, and rendering for
deeply nested promoted widgets.

## Changes

- **What**: Stabilize nested subgraph promoted widget resolution chain
- Use deep source keys for promoted widget values in Vue rendering mode
- Resolve effective widget options from the source widget instead of the
promoted view
  - Stabilize slot resolution for nested promoted widgets
  - Preserve combo value rendering for promoted subgraph widgets
- Prevent subgraph definition deletion while other nodes still reference
the same type
  - Clean up unused exported resolution types

## Review Focus

- `resolveConcretePromotedWidget.ts` — new recursive resolution logic
for deeply nested promoted widgets
- `useGraphNodeManager.ts` — option extraction now uses
`effectiveWidget` for promoted widgets
- `SubgraphNode.ts` — unpack no longer force-deletes definitions
referenced by other nodes

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9282-fix-stabilize-nested-subgraph-promoted-widget-resolution-3146d73d365081208a4fe931bb7569cf)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

src/core/graph/subgraph/resolveSubgraphInputTarget.ts

@@ -0,0 +1,34 @@
+import type { LGraphNode } from '@/lib/litegraph/src/litegraph'
+
+import { resolveSubgraphInputLink } from './resolveSubgraphInputLink'
+
+type ResolvedSubgraphInputTarget = {
+  nodeId: string
+  widgetName: string
+}
+
+export function resolveSubgraphInputTarget(
+  node: LGraphNode,
+  inputName: string
+): ResolvedSubgraphInputTarget | undefined {
+  return resolveSubgraphInputLink(
+    node,
+    inputName,
+    ({ inputNode, targetInput, getTargetWidget }) => {
+      if (inputNode.isSubgraphNode()) {
+        return {
+          nodeId: String(inputNode.id),
+          widgetName: targetInput.name
+        }
+      }
+
+      const targetWidget = getTargetWidget()
+      if (!targetWidget) return undefined
+
+      return {
+        nodeId: String(inputNode.id),
+        widgetName: targetWidget.name
+      }
+    }
+  )
+}