feat(frontend): drive seek bar with rAF for smooth playback progress

frontend/src/lib/components/player/SeekBar.svelte

@@ -19,11 +19,11 @@
 		class="group relative h-1.5 flex-1 cursor-pointer rounded-full bg-[var(--mf-track)] transition-[height] hover:h-2"
 	>
 		<div
-			class="absolute inset-y-0 left-0 rounded-full bg-[var(--mf-accent)] transition-[width] duration-75 ease-linear group-hover:brightness-110"
+			class="absolute inset-y-0 left-0 rounded-full bg-[var(--mf-accent)] group-hover:brightness-110"
 			style="width:{player.progressPercent}%"
 		></div>
 		<span
-			class="pointer-events-none absolute top-1/2 h-3 w-3 -translate-x-1/2 -translate-y-1/2 rounded-full bg-white opacity-0 shadow-[0_1px_4px_rgba(0,0,0,0.5)] transition-[left,opacity] duration-75 ease-linear group-hover:opacity-100"
+			class="pointer-events-none absolute top-1/2 h-3 w-3 -translate-x-1/2 -translate-y-1/2 rounded-full bg-white opacity-0 shadow-[0_1px_4px_rgba(0,0,0,0.5)] transition-opacity duration-75 group-hover:opacity-100"
 			style="left:{player.progressPercent}%"
 		></span>
 	</button>

frontend/src/lib/player/player.svelte.ts

@@ -61,6 +61,7 @@ class PlayerState {
 	#audio: HTMLAudioElement | null = null;
 	#loadToken = 0;
 	#accentCache = new Map<string, Accent>();
+	#rafId: number | null = null;
 
 	current = $derived(this.tracks.find((t) => t.id === this.currentId) ?? EMPTY);
 	accent = $derived(this.accentColor ?? accentForHue(this.current.hue));
@@ -79,15 +80,22 @@ class PlayerState {
 		const audio = new Audio();
 		audio.preload = 'auto';
 		audio.volume = this.volume / 100;
-		audio.addEventListener('timeupdate', () => {
-			this.progress = audio.currentTime;
-		});
 		audio.addEventListener('durationchange', () => this.#syncDuration(audio.duration));
 		audio.addEventListener('loadedmetadata', () => this.#syncDuration(audio.duration));
-		audio.addEventListener('play', () => (this.playing = true));
-		audio.addEventListener('pause', () => (this.playing = false));
-		audio.addEventListener('ended', () => this.next());
+		audio.addEventListener('play', () => {
+			this.playing = true;
+			this.#startProgressLoop();
+		});
+		audio.addEventListener('pause', () => {
+			this.playing = false;
+			this.#stopProgressLoop();
+		});
+		audio.addEventListener('ended', () => {
+			this.#stopProgressLoop();
+			this.next();
+		});
 		audio.addEventListener('error', () => {
+			this.#stopProgressLoop();
 			this.loading = false;
 			this.playing = false;
 			this.error = 'No se pudo reproducir la pista.';
@@ -96,6 +104,24 @@ class PlayerState {
 		return audio;
 	}
 
+	#tickProgress = () => {
+		const audio = this.#audio;
+		if (!audio) return;
+		this.progress = audio.currentTime;
+		this.#rafId = requestAnimationFrame(this.#tickProgress);
+	};
+
+	#startProgressLoop() {
+		if (this.#rafId !== null) return;
+		this.#rafId = requestAnimationFrame(this.#tickProgress);
+	}
+
+	#stopProgressLoop() {
+		if (this.#rafId === null) return;
+		cancelAnimationFrame(this.#rafId);
+		this.#rafId = null;
+	}
+
 	#syncDuration(value: number) {
 		if (!Number.isFinite(value) || value <= 0) return;
 		const id = this.currentId;