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/TransportControls.svelte

@@ -0,0 +1,47 @@
+<script lang="ts">
+	import { player } from '$lib/player/player.svelte';
+</script>
+
+<div class="flex items-center gap-5">
+	<button
+		type="button"
+		onclick={() => player.previous()}
+		aria-label="Anterior"
+		class="flex text-fg opacity-70 transition hover:opacity-100 active:scale-90"
+	>
+		<svg width="16" height="14" viewBox="0 0 16 14" fill="currentColor">
+			<rect x="0" y="0" width="2.5" height="14" rx="1" />
+			<path d="M15 0 5 7l10 7z" />
+		</svg>
+	</button>
+
+	<button
+		type="button"
+		onclick={() => player.toggle()}
+		aria-label={player.playing ? 'Pausar' : 'Reproducir'}
+		class="grid h-[36px] w-[36px] place-items-center rounded-full bg-fg text-bg shadow-lg transition duration-100 active:scale-95"
+	>
+		{#if player.playing}
+			<svg width="12" height="12" viewBox="0 0 12 12" fill="currentColor">
+				<rect x="1.5" y="0" width="3.5" height="12" rx="1" />
+				<rect x="7" y="0" width="3.5" height="12" rx="1" />
+			</svg>
+		{:else}
+			<svg width="12" height="12" viewBox="0 0 12 12" fill="currentColor">
+				<path d="M2.5 0 12 6l-9.5 6z" />
+			</svg>
+		{/if}
+	</button>
+
+	<button
+		type="button"
+		onclick={() => player.next()}
+		aria-label="Siguiente"
+		class="flex text-fg opacity-70 transition hover:opacity-100 active:scale-90"
+	>
+		<svg width="16" height="14" viewBox="0 0 16 14" fill="currentColor">
+			<path d="M1 0 11 7 1 14z" />
+			<rect x="13.5" y="0" width="2.5" height="14" rx="1" />
+		</svg>
+	</button>
+</div>