feat: bring over the albums, explore and player work from the worktree

Moves the remaining uncommitted work: the home gets quick mixes and a
"Tus álbumes" shelf, saving a YouTube album now goes through
addYoutubeAlbumToPlaylistAction instead of the SaveYouTubeAlbum command,
and UserAlbum drops its unused ExternalId.

The mixes section keeps its current shape (no refresh action, no badge,
hidden when empty) rather than the older version the worktree carried.

web-player/src/lib/player/player.svelte.ts

@@ -75,6 +75,15 @@ export function toQueueItems(tracks: ApiTrackLike[]): QueueItem[] {
 	});
 }
 
+async function readErrorMessage(res: Response): Promise<string> {
+	try {
+		const body = (await res.json()) as { message?: string };
+		return body?.message || `Error ${res.status}`;
+	} catch {
+		return `Error ${res.status}`;
+	}
+}
+
 const RECENT_LIMIT = 15;
 
 const EMPTY: PlayerTrack = {
@@ -286,13 +295,16 @@ class PlayerState {
 			if (token !== this.#loadToken) return;
 			this.loading = false;
 			this.playing = false;
-			this.error = 'No se pudo reproducir la pista.';
+			this.error =
+				exception instanceof Error && exception.message
+					? exception.message
+					: 'No se pudo reproducir la pista.';
 		}
 	}
 
 	async #resolveLocalSrc(id: string): Promise<string> {
 		const res = await fetch(`/api/tracks/${id}/stream`);
-		if (!res.ok) throw new Error(String(res.status));
+		if (!res.ok) throw new Error(await readErrorMessage(res));
 		const { manifestUrl, ticket } = (await res.json()) as {
 			manifestUrl: string;
 			ticket: string;
@@ -302,7 +314,7 @@ class PlayerState {
 
 	async #resolveYouTubeSrc(videoId: string): Promise<string> {
 		const res = await fetch(`/api/youtube/tracks/${videoId}/stream`);
-		if (!res.ok) throw new Error(String(res.status));
+		if (!res.ok) throw new Error(await readErrorMessage(res));
 		const { mode, streamUrl, ticket } = (await res.json()) as {
 			mode: string;
 			streamUrl: string;