feat(web-player): rebuild Inicio and Buscar to the design handoff

Applies the handoff's layout and image shapes while keeping the current
Musify design system (Inter, colors, tokens) — no font or palette swap.

Inicio now stacks distinct shelves instead of repeated square grids:
recently played rows, a rail of recently listened albums with an "Álbum"
badge, a "Hecho para ti" bento of mixes, a rail of playlists with a
trailing dashed "Ver todas" tile, tall "Canciones nuevas" posters with a
"Nuevo" badge, a rail of circular top-artist avatars, and a recommended
rail. Buscar splits into Álbumes (square cards + badge), Usuarios (a
circular-avatar directory) and a flat Canciones list.

Top artists and the search user directory are filler data until the
backend exposes them. New shared pieces: Rail, CoverBadge, ArtistAvatar,
MixBentoTile. The orphaned TrackTile and MixCard are removed.

web-player/src/lib/components/ui/SectionHeading.svelte

@@ -12,11 +12,11 @@
 
 {#if actions}
 	<div class="mb-3 flex items-baseline justify-between gap-4 sm:mb-4 {klass}">
-		<h2 class="text-lg font-semibold tracking-tight text-fg sm:text-xl">{title}</h2>
+		<h2 class="text-lg tracking-tight text-fg sm:text-[28px]">{title}</h2>
 		{@render actions()}
 	</div>
 {:else}
-	<h2 class="mb-3 text-lg font-semibold tracking-tight text-fg sm:mb-4 sm:text-xl {klass}">
+	<h2 class="mb-3 text-lg tracking-tight text-fg sm:mb-4 sm:text-[28px] {klass}">
 		{title}
 	</h2>
 {/if}