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/IconButton.svelte

@@ -0,0 +1,37 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	interface Props {
+		label: string;
+		type?: 'button' | 'submit';
+		size?: 'sm' | 'md';
+		revealOnHover?: boolean;
+		onclick?: (event: MouseEvent) => void;
+		class?: string;
+		children: Snippet;
+	}
+
+	let {
+		label,
+		type = 'button',
+		size = 'md',
+		revealOnHover = false,
+		onclick,
+		class: klass = '',
+		children
+	}: Props = $props();
+
+	const sizes = { sm: 'h-7 w-7', md: 'h-8 w-8' };
+</script>
+
+<button
+	{type}
+	{onclick}
+	aria-label={label}
+	title={label}
+	class="grid place-items-center rounded-control text-muted transition hover:bg-hover hover:text-fg {sizes[
+		size
+	]} {revealOnHover ? 'opacity-0 group-hover:opacity-100 focus-visible:opacity-100' : ''} {klass}"
+>
+	{@render children()}
+</button>