music: Music Player widget + app-wide player dock

The widget browses the /api/music/* library (search albums → tracklist) and hands
a queue to an app-wide player. The player (useMusicPlayer, useGlobal-backed) and
its site-wide bottom dock (MusicPlayerHost) live in the persistent DashboardLayout,
so playback survives route changes. Dock has cover/title/artist, drag-scrubbing
(SeekBar), volume (persisted), and prev/play/next/close. The nav Dock slides up by
MUSIC_DOCK_HEIGHT while the music dock is present.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/apps/officer-web/Screens/Dashboard/Layout/DashboardLayout.tsx

@@ -1,4 +1,4 @@
-import { useDock } from 'officerdev';
+import { useDock, MusicPlayerHost } from 'officerdev';
 import { Background } from './Background';
 import { Header } from './Header';
 import { Dock, ALL_DOCK_ITEMS, DEFAULT_DOCK_PATHS } from './Dock';
@@ -23,6 +23,7 @@ export function DashboardLayout({ children }: DashboardLayoutProps) {
           {children}
         </div>
       </section>
+      <MusicPlayerHost />
     </div>
   );
 };