refactor(kiwi)!: drop the colorVariableBinding paint field

`fig.kiwi` never defined the field, so nothing Figma writes carries one
and nothing OpenPencil writes has since `colorVar` replaced it. What
remained were readers kept so that files written by earlier OpenPencil
builds still restored their bindings — a compatibility path the project
does not keep before 1.0.

The field, the `VariableBinding` type and both readers are gone.
Reopening one of those files leaves the paint's colour unbound; binding
it again records it the way Figma does.

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Breaking changes
 
+- `VariableBinding` and the `colorVariableBinding` paint field are gone from `@open-pencil/core`, `@open-pencil/core/kiwi`, and the Kiwi `Paint` type. `fig.kiwi` never defined the field, so only `.fig` files OpenPencil itself wrote before `colorVar` contain one; reopening such a file leaves the paint's colour unbound, and binding it again records it the way Figma does.
 - `encodeNodeChangeWithVariables`, `encodePaintWithVariableBinding`, and `encodeVarint` are removed from `@open-pencil/core` and `@open-pencil/core/kiwi`. They spliced a colour-variable binding into encoded bytes because the field had no schema entry; exports now write `colorVar`, which `fig.kiwi` defines, so nothing needs them. `parseVariableId` is unchanged.
 - The desktop app now requires macOS 13 or later; the web app supports Chrome 111, Edge 111, Firefox 128, and Safari 16.4 or later.
 - `.fig` reading moved to one reader, so the previous importer's exports are gone. `importNodeChanges` (`@open-pencil/core` and `@open-pencil/core/kiwi`) and `importClipboardNodes` (`@open-pencil/fig/clipboard`) are replaced by `parseFigFile` and `parseFigmaClipboard`; `populateLazyFigImportRoots` and `populateAllLazyFigImportRoots` (`@open-pencil/core/kiwi`) are replaced by `populateFigPage` and `populateAllFigPages` on `@open-pencil/core/io/formats/fig`; `populateAndApplyOverrides` (`@open-pencil/fig/instance-overrides`) is replaced by `interpretInstance` with `materializeInstance`. `FIG_PACKAGE_STATUS` now reads `document-reader`, and `assertFigPackageReady()` is gone, because `@open-pencil/fig` reads an archive into a SceneGraph itself rather than directing callers to Core.

packages/core/src/index.ts

@@ -341,7 +341,6 @@ export {
   type Color as KiwiColor,
   type Paint as KiwiPaint,
   type Effect as KiwiEffect,
-  type VariableBinding,
   type ParentIndex,
   type FigmaMessage,
   MESSAGE_TYPES,

packages/core/src/kiwi/index.ts

@@ -19,7 +19,6 @@ export {
   type Color,
   type Paint,
   type Effect,
-  type VariableBinding,
   type VariableAnyValue,
   type VariableDataEntry,
   type VariableConsumptionEntry,

packages/fig/src/instance-overrides/materialize-instance.ts

@@ -185,7 +185,7 @@ function recordPaintBindingClaims(
   if (!Array.isArray(paints)) return
   let declared = false
   for (const [index, paint] of paints.entries()) {
-    const alias = (paint as Paint).colorVar?.value?.alias ?? (paint as Paint).colorVariableBinding
+    const alias = (paint as Paint).colorVar?.value?.alias
     if (!alias) continue
     const field = `boundVariables/${scene}/${index}/color`
     setInstanceOverride(

packages/fig/src/node-change/export/context.ts

@@ -181,8 +181,8 @@ export function applyColorVariableBinding(
   // An imported paint carries the binding it arrived with. Unbinding the field has to clear
   // it, or the export hands Figma back a variable the document no longer references.
   if (!variableId) {
-    if (!paint.colorVar && !paint.colorVariableBinding) return paint
-    const { colorVar: _unbound, colorVariableBinding: _legacy, ...unbound } = paint
+    if (!paint.colorVar) return paint
+    const { colorVar: _cleared, ...unbound } = paint
     return unbound
   }
   return {

packages/fig/src/node-change/plugin-data.ts

@@ -141,13 +141,11 @@ export function extractBoundVariables(nc: NodeChange): Record<string, string> {
     }
   }
   nc.fillPaints?.forEach((paint, i) => {
-    const variableGuid =
-      paint.colorVariableBinding?.variableID ?? paint.colorVar?.value?.alias?.guid
+    const variableGuid = paint.colorVar?.value?.alias?.guid
     if (variableGuid) bindings[`fills/${i}/color`] = guidToString(variableGuid)
   })
   nc.strokePaints?.forEach((paint, i) => {
-    const variableGuid =
-      paint.colorVariableBinding?.variableID ?? paint.colorVar?.value?.alias?.guid
+    const variableGuid = paint.colorVar?.value?.alias?.guid
     if (variableGuid) bindings[`strokes/${i}/color`] = guidToString(variableGuid)
   })
   return bindings

packages/kiwi/src/fig/codec.ts

@@ -105,10 +105,6 @@ export interface ParentIndex {
   position: string
 }
 
-export interface VariableBinding {
-  variableID: GUID
-}
-
 export interface ImageSource {
   hash: string | Uint8Array
   name?: string
@@ -150,7 +146,6 @@ export interface Paint {
   density?: number
   noiseSize?: Vector
   customEffectId?: { guid?: GUID }
-  colorVariableBinding?: VariableBinding
   colorVar?: {
     value?: {
       alias?: {