feat(audio): add voice selector, voice samples, MediaSession cover art, and fix speed/voice bug

- Fix speed/voice bug: AudioPlayer no longer accepts speed/voice as props;
  startPlayback() reads audioStore.voice/speed directly instead of overwriting them
- Add GET /api/voices endpoint (Go) proxying Kokoro, cached in-memory
- Add POST /api/audio/voice-samples endpoint (Go) to pre-generate sample clips
  for all voices and store them in MinIO under _voice-samples/{voice}.mp3
- Add GET /api/presign/voice-sample/{voice} endpoint (Go)
- Add SvelteKit proxy routes: /api/voices, /api/presign/voice-sample, /api/audio/voice-samples
- Add presignVoiceSample() helper in minio.ts with proper host rewrite
- Pass book.cover through +page.server.ts -> +page.svelte -> AudioPlayer
- Set navigator.mediaSession.metadata on playback start so cover art,
  book title, and chapter title appear on phone lock screen / notification

ui/src/routes/api/audio/voice-samples/+server.ts

@@ -0,0 +1,33 @@
+import { json } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { env } from '$env/dynamic/private';
+
+const SCRAPER_URL = env.SCRAPER_API_URL ?? 'http://localhost:8080';
+
+/**
+ * POST /api/audio/voice-samples
+ * Triggers generation of voice sample audio files for all (or specified) voices.
+ * Proxies to the scraper's POST /api/audio/voice-samples endpoint.
+ * Optional body: { voices: string[] } to generate a subset.
+ * Returns: { generated: string[], skipped: string[], failed: string[] }
+ */
+export const POST: RequestHandler = async ({ request }) => {
+	let body: { voices?: string[] } = {};
+	try {
+		body = await request.json();
+	} catch {
+		// Empty body is fine — generates all voices
+	}
+
+	try {
+		const res = await fetch(`${SCRAPER_URL}/api/audio/voice-samples`, {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify(body)
+		});
+		const data = await res.json();
+		return json(data, { status: res.ok ? 200 : res.status });
+	} catch (e) {
+		return json({ error: String(e) }, { status: 502 });
+	}
+};

ui/src/routes/api/presign/voice-sample/+server.ts

@@ -0,0 +1,26 @@
+import { json, error } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { presignVoiceSample } from '$lib/server/minio';
+
+/**
+ * GET /api/presign/voice-sample?voice=af_bella
+ * Returns a presigned URL for the voice sample audio file.
+ * Returns 404 if the sample has not been generated yet.
+ */
+export const GET: RequestHandler = async ({ url }) => {
+	const voice = url.searchParams.get('voice');
+	if (!voice) {
+		error(400, 'Missing voice parameter');
+	}
+
+	try {
+		const presignedUrl = await presignVoiceSample(voice);
+		return json({ url: presignedUrl });
+	} catch (e) {
+		const status = (e as { status?: number }).status;
+		if (status === 404) {
+			error(404, 'Voice sample not found');
+		}
+		error(502, `Failed to presign voice sample: ${e}`);
+	}
+};

ui/src/routes/api/voices/+server.ts

@@ -0,0 +1,23 @@
+import { json } from '@sveltejs/kit';
+import type { RequestHandler } from './$types';
+import { env } from '$env/dynamic/private';
+
+const SCRAPER_URL = env.SCRAPER_API_URL ?? 'http://localhost:8080';
+
+/**
+ * GET /api/voices
+ * Proxies the voice list from the scraper → Kokoro.
+ * Returns { voices: string[] }
+ */
+export const GET: RequestHandler = async () => {
+	try {
+		const res = await fetch(`${SCRAPER_URL}/api/voices`);
+		if (!res.ok) {
+			return json({ voices: [] });
+		}
+		const data = (await res.json()) as { voices: string[] };
+		return json({ voices: data.voices ?? [] });
+	} catch {
+		return json({ voices: [] });
+	}
+};

ui/src/routes/books/[slug]/chapters/[n]/+page.server.ts

@@ -4,6 +4,9 @@ import type { PageServerLoad } from './$types';
 import { getBook, listChapterIdx } from '$lib/server/pocketbase';
 import { presignChapter } from '$lib/server/minio';
 import { log } from '$lib/server/logger';
+import { env } from '$env/dynamic/private';
+
+const SCRAPER_URL = env.SCRAPER_API_URL ?? 'http://localhost:8080';
 
 export const load: PageServerLoad = async ({ params, locals }) => {
 	const { slug } = params;
@@ -11,14 +14,29 @@ export const load: PageServerLoad = async ({ params, locals }) => {
 
 	if (!n || n < 1) error(400, 'Invalid chapter number');
 
-	// Fetch book metadata and chapter index in parallel
-	const [book, chapters] = await Promise.all([getBook(slug), listChapterIdx(slug)]);
+	// Fetch book metadata, chapter index, and voice list in parallel
+	const [book, chapters, voicesRes] = await Promise.all([
+		getBook(slug),
+		listChapterIdx(slug),
+		fetch(`${SCRAPER_URL}/api/voices`).catch(() => null)
+	]);
 
 	if (!book) error(404, `Book "${slug}" not found`);
 
 	const chapterIdx = chapters.find((c) => c.number === n);
 	if (!chapterIdx) error(404, `Chapter ${n} not found`);
 
+	// Parse voices — fall back to a minimal default list on error
+	let voices: string[] = [];
+	try {
+		if (voicesRes?.ok) {
+			const data = (await voicesRes.json()) as { voices: string[] };
+			voices = data.voices ?? [];
+		}
+	} catch {
+		// Non-critical — UI will use store default
+	}
+
 	// Get presigned URL and fetch chapter markdown server-side
 	let html = '';
 	try {
@@ -36,9 +54,10 @@ export const load: PageServerLoad = async ({ params, locals }) => {
 	const nextChapter = chapters.find((c) => c.number === n + 1) ?? null;
 
 	return {
-		book: { slug: book.slug, title: book.title },
+		book: { slug: book.slug, title: book.title, cover: book.cover ?? '' },
 		chapter: chapterIdx,
 		html,
+		voices,
 		prev: prevChapter ? prevChapter.number : null,
 		next: nextChapter ? nextChapter.number : null,
 		sessionId: locals.sessionId

ui/src/routes/books/[slug]/chapters/[n]/+page.svelte

@@ -72,7 +72,9 @@
 	chapter={data.chapter.number}
 	chapterTitle={data.chapter.title || `Chapter ${data.chapter.number}`}
 	bookTitle={data.book.title}
+	cover={data.book.cover}
 	nextChapter={data.next}
+	voices={data.voices}
 />
 
 <!-- Chapter content -->