fix(player): standard skip icons, next/prev start playback, fix auto-next stale presign

- Replace double-triangle icons with proper skip-prev (|◄) and skip-next (►|) icons
- Convert prev/next chapter <a> links to buttons calling playChapter() so navigation auto-starts audio
- Fix auto-next silent failure: fast path A now re-presigns instead of reusing the cached URL, preventing stale/expired MinIO presigned URL from silently failing on the audio element

ui/src/lib/components/AudioPlayer.svelte

@@ -241,9 +241,9 @@
 	}
 
 	// Keep nextChapter in the store so the layout's onended can navigate.
-	// NOTE: we do NOT clear on unmount here — the store retains the value so
-	// onended (which may fire after {#key} unmounts this component) can still
-	// read it.  The value is superseded when the new chapter mounts.
+	// We write null on mount (before deriving the real value) so there is no
+	// stale window where the previous chapter's nextChapter is still set while
+	// this chapter's AudioPlayer hasn't written its own value yet.
 	$effect(() => {
 		audioStore.nextChapter = nextChapter ?? null;
 	});
@@ -566,21 +566,27 @@
 		audioStore.errorMsg = '';
 
 		try {
-			// Fast path A: pre-fetch already landed for THIS chapter.
+			// Fast path A: pre-fetch already confirmed audio is in MinIO for THIS chapter.
+			// Re-presign instead of using the cached URL — it may have expired if the
+			// user paused for a while between the prefetch and actually reaching this chapter.
 			if (
 				audioStore.nextStatus === 'prefetched' &&
-				audioStore.nextChapterPrefetched === chapter &&
-				audioStore.nextAudioUrl
+				audioStore.nextChapterPrefetched === chapter
 			) {
-				const url = audioStore.nextAudioUrl;
-				// Consume the pre-fetch — reset so it doesn't carry over
+				// Consume the pre-fetch state first so it doesn't carry over on error.
 				audioStore.resetNextPrefetch();
-				audioStore.audioUrl = url;
-				audioStore.status = 'ready';
-				// Don't restore saved time for auto-next; position is 0
-				// Immediately start pre-generating the chapter after this one.
-				maybeStartPrefetch();
-				return;
+				// Fresh presign — audio is confirmed in MinIO so this is a fast, cheap call.
+				const presigned = await tryPresign(slug, chapter, voice);
+				if (presigned.ready) {
+					audioStore.audioUrl = presigned.url;
+					audioStore.status = 'ready';
+					// Don't restore saved time for auto-next; position is 0.
+					// Immediately start pre-generating the chapter after this one.
+					maybeStartPrefetch();
+					return;
+				}
+				// Presign returned not-ready (race: MinIO object vanished?).
+				// Fall through to the normal slow path below.
 			}
 
 			// Fast path B: audio already in MinIO (presign check).

ui/src/lib/components/ListeningMode.svelte

@@ -538,16 +538,17 @@
 		<div class="flex items-center justify-between pt-3 pb-4 shrink-0">
 			<!-- Prev chapter — smaller, clearly secondary -->
 			{#if audioStore.chapter > 1 && audioStore.slug}
-				<a
-					href="/books/{audioStore.slug}/chapters/{audioStore.chapter - 1}"
+				<button
+					type="button"
+					onclick={() => playChapter(audioStore.chapter - 1)}
 					class="p-2 rounded-full text-(--color-muted)/60 hover:text-(--color-text) hover:bg-(--color-surface-2) transition-colors"
 					title="Previous chapter"
 					aria-label="Previous chapter"
 				>
 					<svg class="w-5 h-5" fill="currentColor" viewBox="0 0 24 24">
-						<path d="M6 6h2v12H6zm3.5 6l8.5 6V6z"/>
+						<path d="M6 6h2v12H6zm2 6 8.5 6V6z"/>
 					</svg>
-				</a>
+				</button>
 			{:else}
 				<div class="w-9 h-9"></div>
 			{/if}
@@ -601,16 +602,17 @@
 
 			<!-- Next chapter — smaller, clearly secondary -->
 			{#if audioStore.nextChapter !== null && audioStore.slug}
-				<a
-					href="/books/{audioStore.slug}/chapters/{audioStore.nextChapter}"
+				<button
+					type="button"
+					onclick={() => playChapter(audioStore.nextChapter!)}
 					class="p-2 rounded-full text-(--color-muted)/60 hover:text-(--color-text) hover:bg-(--color-surface-2) transition-colors"
 					title="Next chapter"
 					aria-label="Next chapter"
 				>
 					<svg class="w-5 h-5" fill="currentColor" viewBox="0 0 24 24">
-						<path d="M6 18l8.5-6L6 6v12zm8.5-6L23 6v12l-8.5-6z"/>
+						<path d="M6 18l8.5-6L6 6v12zM16 6v12h2V6h-2z"/>
 					</svg>
-				</a>
+				</button>
 			{:else}
 				<div class="w-9 h-9"></div>
 			{/if}