refactor: rename frontend/ to web-player/ and format with prettier

Updates the compose build context, the Dockerfile header, the package
name and the docs. The compose service and container keep the name
frontend/musify-frontend, since nginx routes to http://frontend:3000.

The source files also carry the first prettier pass, so the rename and
the reformat land together for them.

web-player/src/lib/components/player/PlayerBar.svelte

@@ -0,0 +1,23 @@
+<script lang="ts">
+	import TrackInfo from './TrackInfo.svelte';
+	import TransportControls from './TransportControls.svelte';
+	import SeekBar from './SeekBar.svelte';
+	import VolumeControl from './VolumeControl.svelte';
+</script>
+
+<div
+	class="animate-enter fixed right-0 bottom-0 z-50 h-[92px] border-t border-line bg-bg"
+	style="left:var(--mf-sidebar-w)"
+>
+	<div
+		class="grid h-full items-center gap-5 px-8"
+		style="grid-template-columns:minmax(200px,1fr) minmax(0,3fr) minmax(200px,1fr)"
+	>
+		<TrackInfo />
+		<div class="flex flex-col items-center gap-2">
+			<TransportControls />
+			<SeekBar />
+		</div>
+		<VolumeControl />
+	</div>
+</div>