feat: redesign match play and add broadcast tooling

src/lib/components/broadcast/PresetPreview.svelte

@@ -0,0 +1,15 @@
+<script lang="ts">
+	import Overlay from './Overlay.svelte';
+	import { demoChannel, demoPayload } from '$lib/broadcast/demo';
+	import type { Layout, SceneId } from '$lib/broadcast/layout';
+
+	/** A small live render of a layout with the demo match; the checkerboard is where OBS shows through. */
+	const { layout, scene = 'gameplay' }: { layout: Layout; scene?: SceneId } = $props();
+	const payload = $derived(demoPayload(demoChannel(layout), scene));
+</script>
+
+<div
+	class="relative aspect-video overflow-hidden rounded-lg bg-[repeating-conic-gradient(#27272a_0_25%,#18181b_0_50%)] bg-[length:12px_12px]"
+>
+	<Overlay {payload} {scene} />
+</div>