feat: add Painter Node (#8521)

## Summary
Add PainterNode widget for freehand mask drawing directly on the canvas,
with brush/eraser tools, opacity, hardness, and background color
controls.

need BE changes https://github.com/Comfy-Org/ComfyUI/pull/12294

## Screenshots (if applicable)


https://github.com/user-attachments/assets/7222063a-0e40-40bb-b72e-b42c8984beb9



┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8521-feat-add-Painter-Node-2fa6d73d36508124ab2ede449a0cc67a)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/types/widgets.ts

@@ -137,6 +137,7 @@ export type IWidget =
   | IImageCropWidget
   | IBoundingBoxWidget
   | ICurveWidget
+  | IPainterWidget
 
 export interface IBooleanWidget extends IBaseWidget<boolean, 'toggle'> {
   type: 'toggle'
@@ -336,6 +337,11 @@ export interface ICurveWidget extends IBaseWidget<CurvePoint[], 'curve'> {
   value: CurvePoint[]
 }
 
+export interface IPainterWidget extends IBaseWidget<string, 'painter'> {
+  type: 'painter'
+  value: string
+}
+
 /**
  * Valid widget types.  TS cannot provide easily extensible type safety for this at present.
  * Override linkedWidgets[]

src/lib/litegraph/src/widgets/PainterWidget.ts

@@ -0,0 +1,22 @@
+import type { IPainterWidget } from '../types/widgets'
+import { BaseWidget } from './BaseWidget'
+import type { DrawWidgetOptions, WidgetEventOptions } from './BaseWidget'
+
+/**
+ * Widget for the Painter node canvas drawing tool.
+ * This is a widget that only has a Vue widgets implementation.
+ */
+export class PainterWidget
+  extends BaseWidget<IPainterWidget>
+  implements IPainterWidget
+{
+  override type = 'painter' as const
+
+  drawWidget(ctx: CanvasRenderingContext2D, options: DrawWidgetOptions): void {
+    this.drawVueOnlyWarning(ctx, options, 'Painter')
+  }
+
+  onClick(_options: WidgetEventOptions): void {
+    // This is a widget that only has a Vue widgets implementation
+  }
+}

src/lib/litegraph/src/widgets/widgetMap.ts

@@ -21,6 +21,7 @@ import { FileUploadWidget } from './FileUploadWidget'
 import { GalleriaWidget } from './GalleriaWidget'
 import { GradientSliderWidget } from './GradientSliderWidget'
 import { ImageCompareWidget } from './ImageCompareWidget'
+import { PainterWidget } from './PainterWidget'
 import { ImageCropWidget } from './ImageCropWidget'
 import { KnobWidget } from './KnobWidget'
 import { LegacyWidget } from './LegacyWidget'
@@ -58,6 +59,7 @@ export type WidgetTypeMap = {
   imagecrop: ImageCropWidget
   boundingbox: BoundingBoxWidget
   curve: CurveWidget
+  painter: PainterWidget
   [key: string]: BaseWidget
 }
 
@@ -136,6 +138,8 @@ export function toConcreteWidget<TWidget extends IWidget | IBaseWidget>(
       return toClass(BoundingBoxWidget, narrowedWidget, node)
     case 'curve':
       return toClass(CurveWidget, narrowedWidget, node)
+    case 'painter':
+      return toClass(PainterWidget, narrowedWidget, node)
     default: {
       if (wrapLegacyWidgets) return toClass(LegacyWidget, widget, node)
     }