feat(primitives): add menu, dropdown-menu, context-menu, and menubar primitives

Implements WAI-ARIA APG-compliant headless menu primitive families:

- menu: base primitive with MenuRoot, MenuContent, MenuItem,
  MenuCheckboxItem, MenuRadioGroup/Item, MenuSub, and helpers
- dropdown-menu: DropdownMenuRoot with trigger anchoring
- context-menu: ContextMenuRoot with right-click virtual anchor
- menubar: MenubarRoot with keyboard navigation between menus

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

vue/primitives/src/menu/context.ts

@@ -0,0 +1,62 @@
+import type { CheckedState } from './types';
+import type { ComputedRef, Ref, ShallowRef } from 'vue';
+import type { Direction } from '../config-provider';
+
+import { useContextFactory } from '@robonen/vue';
+
+export interface MenuContext {
+  open: Ref<boolean>;
+  onOpenChange: (open: boolean) => void;
+  content: Ref<HTMLElement | null>;
+  onContentChange: (el: HTMLElement | null) => void;
+}
+export const { inject: useMenuContext, provide: provideMenuContext }
+  = useContextFactory<MenuContext>('MenuContext');
+
+export interface MenuRootContext {
+  onClose: () => void;
+  dir: Ref<Direction>;
+  isUsingKeyboardRef: Ref<boolean>;
+  modal: Ref<boolean>;
+}
+export const { inject: useMenuRootContext, provide: provideMenuRootContext }
+  = useContextFactory<MenuRootContext>('MenuRootContext');
+
+export interface MenuContentContext {
+  onItemEnter: (event: PointerEvent) => boolean;
+  onItemLeave: (event: PointerEvent) => void;
+  onTriggerLeave: (event: PointerEvent) => boolean;
+  searchRef: Ref<string>;
+  pointerGraceTimerRef: Ref<number>;
+  onPointerGraceIntentChange: (intent: { area: Array<{ x: number; y: number }>; side: 'left' | 'right' } | null) => void;
+}
+export const { inject: useMenuContentContext, provide: provideMenuContentContext }
+  = useContextFactory<MenuContentContext>('MenuContentContext');
+
+export interface MenuSubContext {
+  contentId: ComputedRef<string>;
+  triggerId: ComputedRef<string>;
+  trigger: ShallowRef<HTMLElement | null>;
+  onTriggerChange: (el: HTMLElement | null) => void;
+}
+export const { inject: useMenuSubContext, provide: provideMenuSubContext }
+  = useContextFactory<MenuSubContext>('MenuSubContext');
+
+export interface MenuRadioGroupContext {
+  modelValue: Ref<string | undefined>;
+  onValueChange: (value: string) => void;
+}
+export const { inject: useMenuRadioGroupContext, provide: provideMenuRadioGroupContext }
+  = useContextFactory<MenuRadioGroupContext>('MenuRadioGroupContext');
+
+export interface MenuItemIndicatorContext {
+  checkedState: Ref<CheckedState>;
+}
+export const { inject: useMenuItemIndicatorContext, provide: provideMenuItemIndicatorContext }
+  = useContextFactory<MenuItemIndicatorContext>('MenuItemIndicatorContext');
+
+export interface MenuGroupContext {
+  id: string;
+}
+export const { inject: useMenuGroupContext, provide: provideMenuGroupContext }
+  = useContextFactory<MenuGroupContext>('MenuGroupContext');