Add anonymous listening support and redesign web-player UI

Backend:
- Expose GET /config/playback so the frontend can detect whether
  anonymous listening is enabled without requiring auth
- Wire anonymous access through track streaming and YouTube resolve flows

Frontend:
- Allow browsing/listening without a session when the backend enables it
- Redesign Inicio, Sidebar and top bar with a new dark theme, typography,
  and layout (top bar with live quick-search, sticky/blurred on scroll)
- Populate Top música, Popular and Recomendados with real Musify +
  YouTube Music data instead of placeholders
- Various shape, spacing, color and animation refinements across the
  redesigned components

web-player/src/lib/server/youtube.ts

@@ -1,5 +1,5 @@
 import type { createApiClient } from '$lib/server/api';
-import type { YouTubeSong } from '$lib/types';
+import type { YouTubeAlbumResult, YouTubeSong } from '$lib/types';
 
 const YOUTUBE_FILLER_QUERIES = [
 	'pop',
@@ -24,6 +24,11 @@ export interface YoutubeFiller {
 	continuationToken: string;
 }
 
+export interface YoutubeAlbumFiller {
+	query: string;
+	items: YouTubeAlbumResult[];
+}
+
 function pickRandomFillerQuery(): string {
 	return YOUTUBE_FILLER_QUERIES[Math.floor(Math.random() * YOUTUBE_FILLER_QUERIES.length)];
 }
@@ -36,9 +41,9 @@ function hash(text: string): number {
 	return Math.abs(h);
 }
 
-function pickFillerQueryForUser(userId: string, date: Date): string {
+function pickFillerQueryForUser(userId: string, date: Date, variant = 0): string {
 	const dayKey = date.toISOString().slice(0, 10);
-	const index = hash(`${userId}:${dayKey}`) % YOUTUBE_FILLER_QUERIES.length;
+	const index = (hash(`${userId}:${dayKey}`) + variant) % YOUTUBE_FILLER_QUERIES.length;
 	return YOUTUBE_FILLER_QUERIES[index];
 }
 
@@ -47,12 +52,13 @@ export async function fetchYoutubeFiller(
 	accessToken: string | null | undefined,
 	limit: number,
 	seedQuery?: string,
-	userId?: string
+	userId?: string,
+	variant = 0
 ): Promise<YoutubeFiller> {
 	if (!accessToken) return { query: '', items: [], continuationToken: '' };
 	const query =
 		seedQuery?.trim() ||
-		(userId ? pickFillerQueryForUser(userId, new Date()) : pickRandomFillerQuery());
+		(userId ? pickFillerQueryForUser(userId, new Date(), variant) : pickRandomFillerQuery());
 	const { data } = await api.GET('/tracks', { params: { query: { name: query, pageSize: 1 } } });
 	const items = (data?.items ?? [])
 		.map((item) => item.youTubeSong)
@@ -63,3 +69,24 @@ export async function fetchYoutubeFiller(
 		continuationToken: data?.nextYoutubeContinuationToken ?? ''
 	};
 }
+
+export async function fetchYoutubeAlbumFiller(
+	api: ReturnType<typeof createApiClient>,
+	accessToken: string | null | undefined,
+	limit: number,
+	seedQuery?: string,
+	userId?: string,
+	variant = 0
+): Promise<YoutubeAlbumFiller> {
+	if (!accessToken) return { query: '', items: [] };
+	const query =
+		seedQuery?.trim() ||
+		(userId ? pickFillerQueryForUser(userId, new Date(), variant) : pickRandomFillerQuery());
+	const { data } = await api.GET('/albums', {
+		params: { query: { title: query, pageNumber: 1, pageSize: limit + 5 } }
+	});
+	const items = (data?.items ?? [])
+		.map((item) => item.youTubeAlbum)
+		.filter((album): album is NonNullable<typeof album> => album !== null && album !== undefined);
+	return { query, items: (items as YouTubeAlbumResult[]).slice(0, limit) };
+}