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/MediaGrid.svelte

@@ -0,0 +1,20 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	interface Props {
+		as?: 'ul' | 'div';
+		min?: string;
+		class?: string;
+		children: Snippet;
+	}
+
+	let { as = 'div', min = '180px', class: klass = '', children }: Props = $props();
+</script>
+
+<svelte:element
+	this={as}
+	class="grid gap-4 {klass}"
+	style="grid-template-columns:repeat(auto-fill,minmax({min},1fr))"
+>
+	{@render children()}
+</svelte:element>