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/Surface.svelte

@@ -0,0 +1,17 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	interface Props {
+		padding?: 'sm' | 'md' | 'lg';
+		class?: string;
+		children: Snippet;
+	}
+
+	let { padding = 'md', class: klass = '', children }: Props = $props();
+
+	const paddings = { sm: 'p-4', md: 'p-5 sm:p-6', lg: 'p-6 sm:p-12' };
+</script>
+
+<div class="rounded-panel bg-surface transition {paddings[padding]} {klass}">
+	{@render children()}
+</div>