Categorize components/ui into primitives, overlay, media, forms and layout

Splits the flat 38-component ui/ folder into primitives/ (generic
controls), overlay/ (menus/modals), media/ (music-domain display
components), forms/ (composite entity forms) and layout/ (page
scaffolding), and updates every import path accordingly.

web-player/src/lib/components/ui/primitives/EmptyState.svelte

@@ -0,0 +1,31 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+	import type { LucideIcon } from '@lucide/svelte';
+
+	interface Props {
+		icon?: LucideIcon;
+		title?: string;
+		description?: string;
+		class?: string;
+		actions?: Snippet;
+	}
+
+	let { icon: Icon, title, description, class: klass = '', actions }: Props = $props();
+</script>
+
+<div class="flex flex-col items-center rounded-panel px-6 py-16 text-center {klass}">
+	{#if Icon}
+		<Icon class="size-icon-xl text-fg-2" strokeWidth={1.25} />
+	{/if}
+	{#if title}
+		<h3 class="mt-6 text-display-3 text-fg">
+			{title}
+		</h3>
+	{/if}
+	{#if description}
+		<p class="mt-2.5 max-w-sm text-sm leading-relaxed text-fg-2">{description}</p>
+	{/if}
+	{#if actions}
+		<div class="mt-6 flex flex-wrap items-center justify-center gap-2.5">{@render actions()}</div>
+	{/if}
+</div>