fix(web-player): follow the API types where they are nullable

The checked-in schema was stale and typed artist, description and externalId
as always present, so the code trusted values the API returns as null. The
regenerated schema tells the truth; the API-shaped types now admit null and it
is normalised on the way into the player, where the state stays non-null.

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

@@ -5,7 +5,7 @@
 	interface Props {
 		id: string;
 		name: string;
-		description?: string;
+		description?: string | null;
 		trackIds: (string | number)[];
 		updatedAt: string;
 		index?: number;