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/ui/PlaylistCard.svelte

@@ -0,0 +1,33 @@
+<script lang="ts">
+	import PlaylistArt from './PlaylistArt.svelte';
+	import { hueFor } from '$lib/theme/color';
+
+	interface Props {
+		id: string;
+		name: string;
+		description?: string;
+		trackIds: (string | number)[];
+		updatedAt: string;
+		index?: number;
+	}
+
+	let { id, name, description, trackIds, updatedAt, index = 0 }: Props = $props();
+</script>
+
+<a
+	href="/playlists/{id}"
+	class="group animate-enter min-w-0 text-left"
+	style="animation-delay:{index * 45}ms"
+>
+	<PlaylistArt
+		playlistId={id}
+		{trackIds}
+		hue={hueFor(id)}
+		version={updatedAt}
+		class="aspect-square w-full rounded-art shadow-art transition group-hover:shadow-art-lg"
+	/>
+	<div class="mt-2.5 truncate text-fg">{name}</div>
+	{#if description}
+		<div class="mt-0.5 truncate text-sm text-fg-3">{description}</div>
+	{/if}
+</a>