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.

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

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

@@ -21,9 +21,7 @@
 		href="/"
 		class="flex items-center gap-2 font-display text-lg font-semibold tracking-[-0.02em] text-fg"
 	>
-		<span
-			class="h-5.5 w-5.5 rounded-[7px] bg-[image:var(--mf-logo-grad)] shadow-[var(--mf-logo-glow)]"
-		></span>
+		<span class="h-5.5 w-5.5 rounded-lg bg-[image:var(--mf-logo-grad)]"></span>
 		Musify
 	</a>