feat: add WidgetValueStore for centralized widget value management (#8594)

## Summary

Implements Phase 1 of the **Vue-owns-truth** pattern for widget values.
Widget values are now canonical in a Pinia store; `widget.value`
delegates to the store while preserving full backward compatibility.

## Changes

- **New store**: `src/stores/widgetValueStore.ts` - centralized widget
value storage with `get/set/remove/removeNode` API
- **BaseWidget integration**: `widget.value` getter/setter now delegates
to store when widget is associated with a node
- **LGraphNode wiring**: `addCustomWidget()` automatically calls
`widget.setNodeId(this.id)` to wire widgets to their nodes
- **Test fixes**: Added Pinia setup to test files that use widgets

## Why

This foundation enables:
- Vue components to reactively bind to widget values via `computed(() =>
store.get(...))`
- Future Yjs/CRDT backing for real-time collaboration
- Cleaner separation between Vue state and LiteGraph rendering

## Backward Compatibility

| Extension Pattern | Status |
|-------------------|--------|
| `widget.value = x` | ✅ Works unchanged |
| `node.widgets[i].value` | ✅ Works unchanged |
| `widget.callback` | ✅ Still fires |
| `node.onWidgetChanged` | ✅ Still fires |

## Testing

- ✅ 4252 unit tests pass
- ✅ Build succeeds

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8594-feat-add-WidgetValueStore-for-centralized-widget-value-management-2fc6d73d36508160886fcb9f3ebd941e)
by [Unito](https://www.unito.io)

---------

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

src/extensions/core/groupNode.ts

@@ -1412,7 +1412,7 @@ export class GroupNodeHandler {
               handlerGroupData.oldToNewWidgetMap[Number(n)]?.[w]
             const widget = this.widgets.find((wg) => wg.name === widgetName)
             if (widget) {
-              widget.type = 'hidden'
+              widget.hidden = true
               widget.computeSize = () => [0, -4]
             }
           }

src/extensions/core/previewAny.ts

@@ -19,14 +19,14 @@ useExtensionService().registerExtension({
 
         const showValueWidget = ComfyWidgets['MARKDOWN'](
           this,
-          'preview',
+          'preview_markdown',
           ['MARKDOWN', {}],
           app
         ).widget as DOMWidget<HTMLTextAreaElement, string>
 
         const showValueWidgetPlain = ComfyWidgets['STRING'](
           this,
-          'preview',
+          'preview_text',
           ['STRING', { multiline: true }],
           app
         ).widget as DOMWidget<HTMLTextAreaElement, string>
@@ -48,6 +48,7 @@ useExtensionService().registerExtension({
           showValueWidgetPlain.options.hidden = value
         }
 
+        showValueWidget.label = 'Preview'
         showValueWidget.hidden = true
         showValueWidget.options.hidden = true
         showValueWidget.options.read_only = true
@@ -55,6 +56,7 @@ useExtensionService().registerExtension({
         showValueWidget.element.disabled = true
         showValueWidget.serialize = false
 
+        showValueWidgetPlain.label = 'Preview'
         showValueWidgetPlain.hidden = false
         showValueWidgetPlain.options.hidden = false
         showValueWidgetPlain.options.read_only = true
@@ -71,7 +73,7 @@ useExtensionService().registerExtension({
           : onExecuted.apply(this, [message])
 
         const previewWidgets =
-          this.widgets?.filter((w) => w.name === 'preview') ?? []
+          this.widgets?.filter((w) => w.name.startsWith('preview_')) ?? []
 
         for (const previewWidget of previewWidgets) {
           const text = message.text ?? ''

src/extensions/core/uploadAudio.ts

@@ -23,6 +23,7 @@ import { getNodeByLocatorId } from '@/utils/graphTraversalUtil'
 
 import { api } from '../../scripts/api'
 import { app } from '../../scripts/app'
+import { useWidgetValueStore } from '@/stores/widgetValueStore'
 
 function updateUIWidget(
   audioUIWidget: DOMWidget<HTMLAudioElement, string>,
@@ -137,9 +138,16 @@ app.registerExtension({
           }
         }
 
-        let value = ''
-        audioUIWidget.options.getValue = () => value
-        audioUIWidget.options.setValue = (v) => (value = v)
+        audioUIWidget.options.getValue = () =>
+          (useWidgetValueStore().getWidget(node.id, inputName)
+            ?.value as string) ?? ''
+        audioUIWidget.options.setValue = (v) => {
+          const widgetState = useWidgetValueStore().getWidget(
+            node.id,
+            inputName
+          )
+          if (widgetState) widgetState.value = v
+        }
 
         return { widget: audioUIWidget }
       }