Promoted subgraph widget changes do not invoke the source node widget callback

### Prerequisites

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

### What happened?

ComfyUI frontend version: 1.50.0 (nightly)
Regression observed since: approximately 1.47.x

Steps to reproduce:
1. Create a custom node with a COMBO widget and assign a widget.callback in a frontend extension.
2. Place the node inside a subgraph.
3. Promote that widget to the subgraph's outer node interface.
4. Change the promoted widget value on the outer subgraph node.

Expected:
Changing the promoted widget invokes the source widget callback, or ComfyUI exposes a supported event/API for custom nodes to react to the change.

Actual:
The inner node's widget.callback is not invoked. The promoted input writes directly to the widget value store, so custom-node logic depending on the original callback does not run.

Impact:
Dependent widget state cannot be refreshed. For example, changing a promoted project selector should fetch and populate a dependent task selector on the inner custom node.

Relevant frontend behavior:
In frontend 1.50.0, promotedInputWidget.callback calls only:
store.setValue(widgetId, next)

It does not forward the change to the source widget callback.

### Steps to Reproduce

1. Create a custom node with a COMBO widget and assign a widget.callback in a frontend extension.
2. Place the node inside a subgraph.
3. Promote that widget to the subgraph's outer node interface.
4. Change the promoted widget value on the outer subgraph node.

### How is this affecting you?

Feature doesn't work as expected

### ComfyUI Frontend Version

1.47.+

### Browser

Chrome/Chromium

### Console Errors

```javascript

```

### Logs

```shell

```

### Additional Context

_No response_

Search the frontend for promotedInputWidget.callback and the store.setValue call described in the issue, then trace how the promoted input relates to its source widget. Reproduce the subgraph and COMBO-widget scenario, and verify that changing the outer value produces the expected callback behavior or supported event/API response.

Written by the indexing model from the issue text.