Subgraph Node (Blueprint) promoted widget values not synced back when changed via ContextMenu (combo/model selection)

### Prerequisites

- [x] I am running the latest version of ComfyUI
- [ ] I have custom nodes enabled

### What happened?

Description：
When using a Subgraph Node (e.g., a Blueprint like "Video Generation (LTX-2.3)"), selecting a value from a COMBO widget's ContextMenu (such as ckpt_name, distilled_lora, etc.) does not correctly update the PromotedWidgetView's internal state. The visual display on the node appears to update, but the actual value used during serialization/execution remains the old default value.
Root Cause：
In bindConcretePointerHandlers, when a concrete widget's onClick handler is triggered (e.g., opening a ContextMenu for a COMBO widget), the user's selection updates the concrete widget's value via BaseWidget.setValue(). However, there is no callback mechanism to propagate this value change back to the PromotedWidgetView's _instanceWidgetValues and widgetValueStore.
The data flow is broken at this point:
User clicks COMBO widget on Subgraph Node
→ concrete widget onClick fires
→ ContextMenu opens
→ User selects a value
→ BaseWidget.setValue(newValue) updates concrete widget
→ ❌ PromotedWidgetView._instanceWidgetValues NOT updated
→ ❌ widgetValueStore NOT updated
→ ❌ Serialization uses stale value

### Steps to Reproduce

1. Create or load a workflow with a Subgraph Node (Blueprint), e.g., "Video Generation (LTX-2.3)"
2. The node has promoted COMBO widgets like ckpt_name, distilled_lora, etc.
3. Click on one of these COMBO widgets (e.g., ckpt_name)
4. Select a different model from the dropdown/ContextMenu
5. The widget visually shows the new value on the node
6. Queue the prompt — the old default value is sent to the backend instead of the newly selected value

Expected Behavior
When a user selects a new value from a COMBO widget's ContextMenu on a Subgraph Node, the selected value should be:

Reflected in the visual display ✅ (this works)
Stored in PromotedWidgetView._instanceWidgetValues ❌ (broken)
Stored in widgetValueStore ❌ (broken)
Used during serialization/execution ❌ (broken)

Suggested Fix：
In bindConcretePointerHandlers, wrap the concrete widget's callback so that when its value changes (via ContextMenu selection or any other mechanism), the new value is propagated back to the PromotedWidgetView:
`// In bindConcretePointerHandlers, after setting up the concrete widget:
const originalCallback = concreteWidget.callback;
concreteWidget.callback = (value: any, ...args: any[]) => {
// Call original callback if exists
if (originalCallback) {
originalCallback(value, ...args);
}
// Sync value back to PromotedWidgetView
promotedWidgetView._instanceWidgetValues[widgetName] = value;
widgetValueStore.setValue(nodeId, widgetName, value);
};`
Alternatively, a watch or Object.defineProperty setter on the concrete widget's value property could be used to detect changes and sync them back

### How is this affecting you?

Crashes ComfyUI completely

### ComfyUI Frontend Version

1.38.14+,confirmed still present in v1.44.4

### Browser

Chrome/Chromium

### Console Errors

```javascript

```

### Logs

```shell

```

### Additional Context

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11297-Subgraph-Node-Blueprint-promoted-widget-values-not-synced-back-when-changed-via-Con-3446d73d3650817d8602c2ba92910b4e) by [Unito](https://www.unito.io)