feat(web): AlbumCard + queue overlay button

Wraps the existing link in a relative container; adds an absolutely
positioned + button. On click stops propagation, fetches /api/albums/:id
once, and feeds tracks into enqueueTracks.

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

@@ -1,9 +1,19 @@
-import { describe, expect, test } from 'vitest';
+import { afterEach, describe, expect, test, vi } from 'vitest';
 import { render, screen, fireEvent } from '@testing-library/svelte';
-import AlbumCard from './AlbumCard.svelte';
-import type { AlbumRef } from '$lib/api/types';
+import type { AlbumRef, AlbumDetail, TrackRef } from '$lib/api/types';
 import { FALLBACK_COVER } from '$lib/media/covers';
 
+vi.mock('$lib/api/client', () => ({
+  api: { get: vi.fn() }
+}));
+vi.mock('$lib/player/store.svelte', () => ({
+  enqueueTracks: vi.fn()
+}));
+
+import AlbumCard from './AlbumCard.svelte';
+import { api } from '$lib/api/client';
+import { enqueueTracks } from '$lib/player/store.svelte';
+
 const album: AlbumRef = {
   id: 'xyz',
   title: 'Kind of Blue',
@@ -15,6 +25,8 @@ const album: AlbumRef = {
   cover_url: '/api/albums/xyz/cover',
 };
 
+afterEach(() => vi.clearAllMocks());
+
 describe('AlbumCard', () => {
   test('renders cover, title, year inside a link to /albums/:id', () => {
     const { container } = render(AlbumCard, { props: { album } });
@@ -29,7 +41,6 @@ describe('AlbumCard', () => {
 
   test('year is omitted when not present', () => {
     render(AlbumCard, { props: { album: { ...album, year: undefined } } });
-    // No crash; no year text.
     expect(screen.queryByText(/1959/)).not.toBeInTheDocument();
   });
 
@@ -39,4 +50,26 @@ describe('AlbumCard', () => {
     await fireEvent.error(img);
     expect(img.src).toBe(FALLBACK_COVER);
   });
+
+  test('+ queue button fetches album detail and calls enqueueTracks', async () => {
+    const tracks: TrackRef[] = [
+      {
+        id: 't1', title: 'So What',
+        album_id: 'xyz', album_title: 'Kind of Blue',
+        artist_id: 'm-davis', artist_name: 'Miles Davis',
+        track_number: 1, disc_number: 1, duration_sec: 545,
+        stream_url: '/api/tracks/t1/stream'
+      }
+    ];
+    const detail: AlbumDetail = { ...album, tracks };
+    (api.get as ReturnType<typeof vi.fn>).mockResolvedValueOnce(detail);
+
+    render(AlbumCard, { props: { album } });
+    await fireEvent.click(screen.getByRole('button', { name: /add to queue/i }));
+
+    expect(api.get).toHaveBeenCalledWith('/api/albums/xyz');
+    await Promise.resolve();
+    await Promise.resolve();
+    expect(enqueueTracks).toHaveBeenCalledWith(tracks);
+  });
 });