fix(primitives): eslint/tsconfig migration, asChild refactor, type fixes

- Migrate to eslint flat config + composite tsconfig.
- Complete the asChild→as="template" refactor (remove asChild prop + :as-child
  bindings across components, matching Primitive's slot model).
- Fix test type errors and source type-safety (useGraceArea hull/point math,
  FocusScope/util ref typing).

Note: ~53 vue-tsc errors remain (HTML attr/event passthrough typing on
transparent wrapper components + a couple of duplicate-export naming
collisions) — not gated by CI (build/lint/test green); pending a
component-attribute-typing design decision.

vue/primitives/src/navigation-menu/__test__/NavigationMenu.landmark.test.ts

@@ -0,0 +1,56 @@
+import type { VueWrapper } from '@vue/test-utils';
+import { mount } from '@vue/test-utils';
+import { afterEach, describe, expect, it } from 'vitest';
+import { defineComponent, h } from 'vue';
+
+import { NavigationMenuList, NavigationMenuRoot } from '../index';
+
+const wrappers: Array<VueWrapper<any>> = [];
+
+afterEach(() => {
+  while (wrappers.length) wrappers.pop()!.unmount();
+  document.body.innerHTML = '';
+});
+
+function track<T extends VueWrapper<any>>(w: T): T {
+  wrappers.push(w);
+  return w;
+}
+
+function mountRoot(attrs: Record<string, unknown> = {}) {
+  const Harness = defineComponent({
+    setup() {
+      return () => h(NavigationMenuRoot, attrs, {
+        default: () => h(NavigationMenuList),
+      });
+    },
+  });
+  return track(mount(Harness, { attachTo: document.body }));
+}
+
+describe('navigation-menu — root landmark a11y', () => {
+  it('renders a <nav> element (implicit role=navigation)', () => {
+    mountRoot();
+    const nav = document.querySelector('nav');
+    expect(nav).toBeTruthy();
+    // <nav> has implicit role="navigation" — no explicit role attribute needed.
+  });
+
+  it('falls back to aria-label="Main" when no label is supplied', () => {
+    mountRoot();
+    const nav = document.querySelector('nav') as HTMLElement;
+    expect(nav.getAttribute('aria-label')).toBe('Main');
+  });
+
+  it('honours a user-supplied aria-label', () => {
+    mountRoot({ 'aria-label': 'Primary site navigation' });
+    const nav = document.querySelector('nav') as HTMLElement;
+    expect(nav.getAttribute('aria-label')).toBe('Primary site navigation');
+  });
+
+  it('exposes data-orientation matching the orientation prop', () => {
+    mountRoot({ orientation: 'vertical' });
+    const nav = document.querySelector('nav') as HTMLElement;
+    expect(nav.getAttribute('data-orientation')).toBe('vertical');
+  });
+});