Add component-level test for DomWidget disabled state logic

## Description

Add a component-level test for the disabled-state logic introduced in DomWidget.vue that verifies the component correctly applies `opacity: 0.5` and `pointerEvents: 'none'` when `positionOverride.widget.computedDisabled` is true.

## Background

The new disabled-state logic is currently only covered by a browser-level E2E test (`subgraphPromotion.spec.ts`). A focused component-level test would provide faster feedback and better isolation for this specific behavior.

## Test Coverage Needed

- Verify `opacity: 0.5` is applied when `positionOverride.widget.computedDisabled` is true
- Verify `pointerEvents: 'none'` is applied when `positionOverride.widget.computedDisabled` is true
- Verify fallback to `widget.computedDisabled` when no position override exists

## Related

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9282
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9282#discussion_r2866949190
- Requested by: @christian-byrne

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-9290-Add-component-level-test-for-DomWidget-disabled-state-logic-3156d73d3650815088a2f711e31e92c3) by [Unito](https://www.unito.io)