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/Checkbox.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+	import Check from '@lucide/svelte/icons/check';
+
+	interface Props {
+		checked?: boolean;
+		name?: string;
+		class?: string;
+		children: Snippet;
+	}
+
+	let { checked = $bindable(false), name, class: klass = '', children }: Props = $props();
+</script>
+
+<label class="flex items-center gap-3 text-base text-fg-2 {klass}">
+	<span class="relative inline-grid h-5 w-5 shrink-0 place-items-center">
+		<input
+			type="checkbox"
+			{name}
+			bind:checked
+			class="peer h-5 w-5 cursor-pointer appearance-none rounded border border-line bg-surface transition checked:border-accent-soft checked:bg-accent-soft focus-visible:border-accent/60 focus-visible:outline-none"
+		/>
+		<Check
+			class="pointer-events-none absolute h-3.5 w-3.5 text-on-accent opacity-0 transition peer-checked:opacity-100"
+			strokeWidth={3}
+		/>
+	</span>
+	<span class="cursor-pointer">{@render children()}</span>
+</label>