web-player: buttons (Button, IconButton, PlayButton)

Button: subtle variants (primary/secondary, left unchanged per the
user's call), glass (formerly secondaryOnGlow, with its own
font-normal), accent, strong (cta-strong/ink, replacing the `!`
overrides on the Home hero), danger. Uses the --color-btn* tokens
instead of bg-[var(--mf-btn-...)]. Radius unified to rounded-control.

IconButton: adds shape (square/round), size (xs/sm/md/lg), tone
(muted/subtle/plain), pressed (aria-pressed + text-accent),
href/reload (links), surface (permanent background + hover to
surface-hover instead of the generic `hover` alias, which matched
surface-2 and gave no contrast).

New PlayButton: a single place for the play/pause SVGs, strong/glass
variants, as="span" for non-interactive overlays. Replaces
TransportControls' main button, the MixTile overlay, and the "Top
result" circle in Explore.

Migrated to IconButton: close queue, "Create playlist" (Sidebar),
Like (TrackInfo, with pressed), queue (PlayerExtras), back (TopBar),
login (MobileHeader), and the row actions in tables (remove/add, size
xs). BackLink uses size-icon-sm and drops a duplicate hover.

Decision (not blocking): remove TopBar's decorative "forward" button
and PlayerExtras' decorative AlignJustify icon (visually dead code).
TransportControls' buttons (shuffle/prev/next/repeat) are
deliberately left unmigrated: they currently have no background or
hit-box of their own, and IconButton always applies a fixed-size
box — migrating them would have added a visible hover pill that
couldn't be verified without Docker this session.

Verified with npm run check/build.

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

@@ -4,6 +4,7 @@
 	import Artwork from '$lib/components/ui/Artwork.svelte';
 	import ExplicitBadge from '$lib/components/ui/ExplicitBadge.svelte';
 	import ArtistLink from '$lib/components/ui/ArtistLink.svelte';
+	import IconButton from '$lib/components/ui/IconButton.svelte';
 	import Heart from '@lucide/svelte/icons/heart';
 
 	interface Props {
@@ -52,14 +53,14 @@
 		/>
 	</div>
 	{#if !compact}
-		<button
-			type="button"
+		<IconButton
+			label={isLiked ? 'Quitar de Me gusta' : 'Añadir a Me gusta'}
+			tone="plain"
+			size="xs"
+			pressed={isLiked}
 			onclick={toggleLike}
-			aria-label={isLiked ? 'Quitar de Me gusta' : 'Añadir a Me gusta'}
-			aria-pressed={isLiked}
-			class="shrink-0 transition hover:opacity-80 {isLiked ? 'text-accent' : 'text-fg-3'}"
 		>
-			<Heart class="h-4 w-4" fill={isLiked ? 'currentColor' : 'none'} strokeWidth={1.7} />
-		</button>
+			<Heart class="size-icon-md" fill={isLiked ? 'currentColor' : 'none'} strokeWidth={1.7} />
+		</IconButton>
 	{/if}
 </div>