Remove YouTube integration from web-player; unify Home track rows

Drops every YouTube-backed route, proxy and type (external
albums/tracks, thumbnail proxy, youtube.ts) and simplifies
player/track/mix types to the local-only catalog now that the
backend contract dropped Source/ExternalId. Genre tiles on Explore
and "Populares esta semana" on Home stay as deliberate client-only
placeholders per product decision, just without the YouTube backing.

Also finishes the design-system unification pass: Home's three
hand-rolled track rows (Continuar escuchando, Playlist destacada,
Populares esta semana) now reuse the shared TrackTitleCell component
instead of duplicating cover+title+artist markup, and the orphaned
Rail.svelte (no importers) is removed.

web-player/src/routes/(app)/albums/[id]/+page.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-	import { player, queueIdForTrack, toQueueItems } from '$lib/player/player.svelte';
+	import { player, toQueueItems } from '$lib/player/player.svelte';
 	import Page from '$lib/components/ui/Page.svelte';
 	import Modal from '$lib/components/ui/Modal.svelte';
 	import Alert from '$lib/components/ui/Alert.svelte';
@@ -19,9 +19,7 @@
 	let editing = $state(false);
 	let confirmingDelete = $state(false);
 
-	const isCurrentQueue = $derived(
-		tracks.some((track) => queueIdForTrack(track) === player.current.id)
-	);
+	const isCurrentQueue = $derived(tracks.some((track) => track.id === player.current.id));
 
 	function playAll() {
 		if (tracks.length === 0) return;