feat(web): TrackMenuItem primitive for M7 #372

Single-entry button used by TrackMenu. Supports aria-disabled (kept
visible to preserve menu height when admin-only or pre-#352 entries
are non-functional) and a `danger` flag for the oxblood-tinted
"Remove from library" entry.

web/src/lib/components/TrackMenuItem.test.ts

@@ -0,0 +1,27 @@
+import { describe, test, expect, vi } from 'vitest';
+import { render, fireEvent, screen } from '@testing-library/svelte';
+import { Music2 } from 'lucide-svelte';
+import TrackMenuItem from './TrackMenuItem.svelte';
+
+describe('TrackMenuItem', () => {
+  test('renders icon, label, and fires onclick', async () => {
+    const onclick = vi.fn();
+    render(TrackMenuItem, { props: { icon: Music2, label: 'Play next', onclick } });
+    const btn = screen.getByRole('menuitem', { name: /play next/i });
+    await fireEvent.click(btn);
+    expect(onclick).toHaveBeenCalledOnce();
+    expect(btn.getAttribute('aria-disabled')).toBe('false');
+  });
+
+  test('aria-disabled blocks onclick and reflects in DOM', async () => {
+    const onclick = vi.fn();
+    render(TrackMenuItem, {
+      props: { icon: Music2, label: 'Add to playlist…', onclick, disabled: true, title: 'Coming with playlists' },
+    });
+    const btn = screen.getByRole('menuitem', { name: /add to playlist/i });
+    expect(btn.getAttribute('aria-disabled')).toBe('true');
+    expect(btn.getAttribute('title')).toBe('Coming with playlists');
+    await fireEvent.click(btn);
+    expect(onclick).not.toHaveBeenCalled();
+  });
+});