[feat] Add context menu converter infrastructure (#7113)

## Summary
- Add `contextMenuConverter.ts` with utilities for converting LiteGraph
context menu items to Vue menu format
- Improve `contextMenuCompat.ts` with set-based diffing for more
reliable legacy extension detection
- Extend `MenuOption`/`SubMenuOption` types with `source`, `disabled`,
`isColorPicker`, and `category` type fields
- Add unit tests for converter functions

## Context
This is foundational work for migrating the node context menu from a
custom Popover-based component to PrimeVue ContextMenu.

The converter provides:
- Menu ordering and section grouping (core items first, then extensions)
- Deduplication with preference for Vue-native items over LiteGraph
items
- Extension categorization with labeled section
- Support for disabled states and color picker submenus

## Test plan
- [x] Unit tests pass for `buildStructuredMenu` (9 tests)
- [x] Unit tests pass for `convertContextMenuToOptions` (7 tests)
- [x] Typecheck passes
- [x] Lint passes
- [x] Knip passes (no unused exports)

## Related
This is PR 1 of 2 for the node context menu migration. PR 2 will wire up
the UI component.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7113-feat-Add-context-menu-converter-infrastructure-2be6d73d3650816ca6c9d2cf50f10159)
by [Unito](https://www.unito.io)

src/composables/graph/useMoreOptionsMenu.ts

@@ -15,10 +15,13 @@ export interface MenuOption {
   icon?: string
   shortcut?: string
   hasSubmenu?: boolean
-  type?: 'divider'
+  type?: 'divider' | 'category'
   action?: () => void
   submenu?: SubMenuOption[]
   badge?: BadgeVariant
+  disabled?: boolean
+  source?: 'litegraph' | 'vue'
+  isColorPicker?: boolean
 }
 
 export interface SubMenuOption {
@@ -26,6 +29,7 @@ export interface SubMenuOption {
   icon?: string
   action: () => void
   color?: string
+  disabled?: boolean
 }
 
 export enum BadgeVariant {