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.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -0,0 +1,62 @@
+<script lang="ts">
+	interface Props {
+		value: number;
+		max: number;
+		label: string;
+		oninput: (value: number) => void;
+		variant: 'seek' | 'volume';
+	}
+
+	let { value, max, label, oninput, variant }: Props = $props();
+
+	const percent = $derived(max > 0 ? (value / max) * 100 : 0);
+
+	function handleInput(event: Event) {
+		oninput(Number((event.currentTarget as HTMLInputElement).value));
+	}
+</script>
+
+<input
+	type="range"
+	min="0"
+	{max}
+	{value}
+	oninput={handleInput}
+	aria-label={label}
+	class="mf-slider mf-slider-{variant}"
+	style="background:linear-gradient(to right, var(--mf-text-2) {percent}%, var(--mf-track) {percent}%)"
+/>
+
+<style>
+	.mf-slider {
+		-webkit-appearance: none;
+		appearance: none;
+		height: var(--mf-range-h);
+		border-radius: 100px;
+		outline: none;
+		cursor: pointer;
+	}
+	.mf-slider-seek {
+		width: 100%;
+	}
+	.mf-slider-volume {
+		width: var(--mf-volume-w);
+	}
+	.mf-slider::-webkit-slider-thumb {
+		-webkit-appearance: none;
+		appearance: none;
+		width: var(--mf-range-thumb);
+		height: var(--mf-range-thumb);
+		border-radius: 50%;
+		background: var(--mf-text);
+		cursor: pointer;
+	}
+	.mf-slider::-moz-range-thumb {
+		width: var(--mf-range-thumb);
+		height: var(--mf-range-thumb);
+		border-radius: 50%;
+		background: var(--mf-text);
+		border: none;
+		cursor: pointer;
+	}
+</style>