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

@@ -16,6 +16,7 @@ import { ButtonWidget } from './ButtonWidget'
 import { ChartWidget } from './ChartWidget'
 import { ColorWidget } from './ColorWidget'
 import { ComboWidget } from './ComboWidget'
+import { CurveWidget } from './CurveWidget'
 import { FileUploadWidget } from './FileUploadWidget'
 import { GalleriaWidget } from './GalleriaWidget'
 import { GradientSliderWidget } from './GradientSliderWidget'
@@ -56,6 +57,7 @@ export type WidgetTypeMap = {
   asset: AssetWidget
   imagecrop: ImageCropWidget
   boundingbox: BoundingBoxWidget
+  curve: CurveWidget
   [key: string]: BaseWidget
 }
 
@@ -132,6 +134,8 @@ export function toConcreteWidget<TWidget extends IWidget | IBaseWidget>(
       return toClass(ImageCropWidget, narrowedWidget, node)
     case 'boundingbox':
       return toClass(BoundingBoxWidget, narrowedWidget, node)
+    case 'curve':
+      return toClass(CurveWidget, narrowedWidget, node)
     default: {
       if (wrapLegacyWidgets) return toClass(LegacyWidget, widget, node)
     }