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/renderer/extensions/vueNodes/widgets/composables/useStringWidget.ts

@@ -4,14 +4,18 @@ import { isStringInputSpec } from '@/schemas/nodeDef/nodeDefSchemaV2'
 import type { InputSpec } from '@/schemas/nodeDef/nodeDefSchemaV2'
 import { app } from '@/scripts/app'
 import type { ComfyWidgetConstructorV2 } from '@/scripts/widgets'
+import { useWidgetValueStore } from '@/stores/widgetValueStore'
 
 const TRACKPAD_DETECTION_THRESHOLD = 50
 
+// TODO: This widget manually syncs with widgetValueStore via getValue/setValue.
+// Consolidate with useMarkdownWidget into shared helpers (domWidgetHelpers.ts).
 function addMultilineWidget(
   node: LGraphNode,
   name: string,
   opts: { defaultVal: string; placeholder?: string }
 ) {
+  const widgetStore = useWidgetValueStore()
   const inputEl = document.createElement('textarea')
   inputEl.className = 'comfy-multiline-input'
   inputEl.value = opts.defaultVal
@@ -20,17 +24,24 @@ function addMultilineWidget(
 
   const widget = node.addDOMWidget(name, 'customtext', inputEl, {
     getValue(): string {
-      return inputEl.value
+      const widgetState = widgetStore.getWidget(node.id, name)
+
+      return (widgetState?.value as string) ?? inputEl.value
     },
     setValue(v: string) {
       inputEl.value = v
+      const widgetState = widgetStore.getWidget(node.id, name)
+      if (widgetState) widgetState.value = v
     }
   })
 
-  widget.inputEl = inputEl
+  widget.element = inputEl
   widget.options.minNodeSize = [400, 200]
 
-  inputEl.addEventListener('input', () => {
+  inputEl.addEventListener('input', (event) => {
+    if (event.target instanceof HTMLTextAreaElement) {
+      widget.value = event.target.value
+    }
     widget.callback?.(widget.value)
   })