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/core/graph/subgraph/proxyWidget.test.ts

@@ -1,4 +1,6 @@
-import { describe, expect, test, vi } from 'vitest'
+import { createTestingPinia } from '@pinia/testing'
+import { setActivePinia } from 'pinia'
+import { beforeEach, describe, expect, test, vi } from 'vitest'
 
 import { registerProxyWidgets } from '@/core/graph/subgraph/proxyWidget'
 import { promoteWidget } from '@/core/graph/subgraph/proxyWidgetUtils'
@@ -43,6 +45,10 @@ function setupSubgraph(
 }
 
 describe('Subgraph proxyWidgets', () => {
+  beforeEach(() => {
+    setActivePinia(createTestingPinia({ stubActions: false }))
+  })
+
   test('Can add simple widget', () => {
     const [subgraphNode, innerNodes] = setupSubgraph(1)
     innerNodes[0].addWidget('text', 'stringWidget', 'value', () => {})

src/core/graph/subgraph/proxyWidget.ts

@@ -115,9 +115,11 @@ const onConfigure = function (
         if (isActiveGraph && w instanceof DOMWidgetImpl) setWidget(w)
         return [w]
       })
-      this.widgets = this.widgets.filter(
-        (w) => !isProxyWidget(w) && !parsed.some(([, name]) => w.name === name)
-      )
+      this.widgets = this.widgets.filter((w) => {
+        if (isProxyWidget(w)) return false
+        const widgetName = w.name
+        return !parsed.some(([, name]) => widgetName === name)
+      })
       this.widgets.push(...newWidgets)
 
       canvasStore.canvas?.setDirty(true, true)
@@ -152,6 +154,7 @@ function newProxyWidget(
     computedHeight: undefined,
     isProxyWidget: true,
     last_y: undefined,
+    label: name,
     name,
     node: subgraphNode,
     onRemove: undefined,

src/core/graph/subgraph/proxyWidgetUtils.ts

@@ -57,15 +57,20 @@ export function demoteWidget(
   widget.promoted = false
 }
 
+function getWidgetName(w: IBaseWidget): string {
+  return isProxyWidget(w) ? w._overlay.widgetName : w.name
+}
+
 export function matchesWidgetItem([nodeId, widgetName]: [string, string]) {
-  return ([n, w]: WidgetItem) => n.id == nodeId && w.name === widgetName
+  return ([n, w]: WidgetItem) =>
+    n.id == nodeId && getWidgetName(w) === widgetName
 }
 export function matchesPropertyItem([n, w]: WidgetItem) {
   return ([nodeId, widgetName]: [string, string]) =>
-    n.id == nodeId && w.name === widgetName
+    n.id == nodeId && getWidgetName(w) === widgetName
 }
 export function widgetItemToProperty([n, w]: WidgetItem): [string, string] {
-  return [`${n.id}`, w.name]
+  return [`${n.id}`, getWidgetName(w)]
 }
 
 function getParentNodes(): SubgraphNode[] {