Checkpoint web-player design-system refactor and backend track genre tagging

Advances the ongoing token/componentization cleanup (anchored player dock,
border-based panels instead of floating shadows, corrected light-mode
accent/gradient tokens) alongside in-progress backend support for track
genre tags.

web-player/src/lib/components/player/SeekBar.svelte

@@ -37,7 +37,7 @@
 			aria-label="Barra de progreso"
 			class="group relative h-3.5 flex-1 cursor-pointer"
 		>
-			<div class="h-[3.5px] w-full overflow-hidden rounded-full bg-track">
+			<div class="h-0.875 w-full overflow-hidden rounded-full bg-track">
 				<div class="h-full rounded-full bg-accent" style="width:{player.progressPercent}%"></div>
 			</div>
 		</button>