Feat: Show Progress Text on Vue Nodes, Markdown for Preview as Text (#6805)

## Summary

Maps the progressText / text preview to a readonly Markdown widget.

## Review Focus

Anything else to tweak about this while I'm in here?

## Screenshots
<img width="1107" height="593" alt="image"
src="https://github.com/user-attachments/assets/a445c07a-2fcb-480c-976e-bda6ff343f14"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6805-Feat-Show-Progress-Text-on-Vue-Nodes-2b26d73d3650814d93c4f2fbf0e00095)
by [Unito](https://www.unito.io)

src/extensions/core/previewAny.ts

@@ -17,10 +17,10 @@ useExtensionService().registerExtension({
       nodeType.prototype.onNodeCreated = function () {
         onNodeCreated ? onNodeCreated.apply(this, []) : undefined
 
-        const showValueWidget = ComfyWidgets['STRING'](
+        const showValueWidget = ComfyWidgets['MARKDOWN'](
           this,
           'preview',
-          ['STRING', { multiline: true }],
+          ['MARKDOWN', {}],
           app
         ).widget as DOMWidget<HTMLTextAreaElement, string>