feat(web): AddToPlaylistMenu submenu wired into TrackMenu (M7 #352)

The "Add to playlist…" entry that #372 reserved as a disabled slot
is now active. Submenu lists the operator's own playlists
alphabetically; "New playlist…" toggles an inline create form that
makes the playlist + appends the track in two API calls.

TrackMenu's existing test asserts the entry is enabled and opens the
submenu instead of the previous "is disabled with tooltip" check.

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

@@ -1,5 +1,5 @@
 import { afterEach, describe, expect, test, vi } from 'vitest';
-import { render, screen, fireEvent } from '@testing-library/svelte';
+import { render, screen, fireEvent, waitFor } from '@testing-library/svelte';
 import { readable } from 'svelte/store';
 import type { TrackRef } from '$lib/api/types';
 
@@ -37,6 +37,13 @@ vi.mock('$lib/api/admin/tracks', () => ({
   removeTrack: vi.fn().mockResolvedValue({ deleted_track_id: 't1' })
 }));
 
+vi.mock('$lib/api/playlists', () => ({
+  createPlaylistsQuery: () =>
+    readable({ data: { owned: [], public: [] }, isPending: false, isError: false }),
+  appendTracks: vi.fn().mockResolvedValue({ id: 'p1', tracks: [] }),
+  createPlaylist: vi.fn().mockResolvedValue({ id: 'p1', name: 'New' })
+}));
+
 vi.mock('$lib/player/store.svelte', () => ({
   playNext: vi.fn(),
   enqueueTrack: vi.fn()
@@ -100,12 +107,15 @@ describe('TrackMenu', () => {
     expect(screen.getAllByRole('menuitem')).toHaveLength(8);
   });
 
-  test('"Add to playlist…" rendered as aria-disabled with tooltip', async () => {
+  test('"Add to playlist…" is enabled and opens the AddToPlaylistMenu submenu', async () => {
     render(TrackMenu, { props: { track } });
     await fireEvent.click(screen.getByRole('button', { name: /track actions/i }));
     const item = screen.getByRole('menuitem', { name: /add to playlist/i });
-    expect(item.getAttribute('aria-disabled')).toBe('true');
-    expect(item.getAttribute('title')).toBe('Coming with playlists');
+    expect(item.getAttribute('aria-disabled')).toBe('false');
+    await fireEvent.click(item);
+    await waitFor(() =>
+      expect(screen.getByRole('menu', { name: /add to playlist/i })).toBeInTheDocument()
+    );
   });
 
   test('"Play next" dispatches playNext(track)', async () => {