feat: add CurveEditor component (#8860)

## Summary
Prerequisite for upcoming native color correction nodes (ColorCurves).

Reusable curve editor with monotone cubic Hermite interpolation,
drag-to-add/move/delete control points, and SVG-based rendering.
Includes CurvePoint type, LUT generation utility, and useCurveEditor
composable for interaction logic.

## Screenshots (if applicable)



https://github.com/user-attachments/assets/948352c7-bdf2-40f9-a8f0-35bc2b2f3202

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8860-feat-add-CurveEditor-component-and-d3-shape-dependency-3076d73d3650817f8421f98e349569d0)
by [Unito](https://www.unito.io)

src/renderer/extensions/vueNodes/widgets/composables/useCurveWidget.ts

@@ -0,0 +1,30 @@
+import type { LGraphNode } from '@/lib/litegraph/src/litegraph'
+import type { ICurveWidget } from '@/lib/litegraph/src/types/widgets'
+import type {
+  CurveInputSpec,
+  InputSpec as InputSpecV2
+} from '@/schemas/nodeDef/nodeDefSchemaV2'
+import type { ComfyWidgetConstructorV2 } from '@/scripts/widgets'
+
+export const useCurveWidget = (): ComfyWidgetConstructorV2 => {
+  return (node: LGraphNode, inputSpec: InputSpecV2): ICurveWidget => {
+    const spec = inputSpec as CurveInputSpec
+    const defaultValue = spec.default ?? [
+      [0, 0],
+      [1, 1]
+    ]
+
+    const rawWidget = node.addWidget(
+      'curve',
+      spec.name,
+      [...defaultValue],
+      () => {}
+    )
+
+    if (rawWidget.type !== 'curve') {
+      throw new Error(`Unexpected widget type: ${rawWidget.type}`)
+    }
+
+    return rawWidget as ICurveWidget
+  }
+}

src/renderer/extensions/vueNodes/widgets/registry/widgetRegistry.ts

@@ -57,6 +57,9 @@ const WidgetImageCrop = defineAsyncComponent(
 const WidgetBoundingBox = defineAsyncComponent(
   () => import('@/components/boundingbox/WidgetBoundingBox.vue')
 )
+const WidgetCurve = defineAsyncComponent(
+  () => import('@/components/curve/WidgetCurve.vue')
+)
 
 export const FOR_TESTING = {
   WidgetButton,
@@ -175,6 +178,14 @@ const coreWidgetDefinitions: Array<[string, WidgetDefinition]> = [
       aliases: ['BOUNDING_BOX'],
       essential: false
     }
+  ],
+  [
+    'curve',
+    {
+      component: WidgetCurve,
+      aliases: ['CURVE'],
+      essential: false
+    }
   ]
 ]
 
@@ -206,7 +217,7 @@ export const shouldRenderAsVue = (widget: Partial<SafeWidgetData>): boolean => {
   return !widget.options?.canvasOnly && !!widget.type
 }
 
-const EXPANDING_TYPES = ['textarea', 'markdown', 'load3D'] as const
+const EXPANDING_TYPES = ['textarea', 'markdown', 'load3D', 'curve'] as const
 
 export function shouldExpand(type: string): boolean {
   const canonicalType = getCanonicalType(type)