add language learner project

Dutch and Korean (explained in English) and English (explained in Dutch)
from A1 to C1, with a Hangul level for Korean. Lessons with notes, words
and sentences generate multiple-choice, typing, sentence building, cloze,
listening and matching exercises. Endless challenges: a seeded daily
challenge, sprint, survival, mixed practice, level tests, spaced-repetition
reviews and generated drills (numbers, clock times, de/het, plurals, Dutch
and Korean conjugation, particles, Hangul reading, irregular verbs).
Progress is stored in localStorage with export/import.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/language-learner/speech.ts

@@ -0,0 +1,43 @@
+/** Text-to-speech through the browser's built-in voices; no audio files or services. */
+
+const supported = () => typeof window !== 'undefined' && 'speechSynthesis' in window;
+
+function voices(): Promise<SpeechSynthesisVoice[]> {
+	if (!supported()) return Promise.resolve([]);
+	const now = speechSynthesis.getVoices();
+	if (now.length) return Promise.resolve(now);
+	return new Promise((resolve) => {
+		const done = () => resolve(speechSynthesis.getVoices());
+		speechSynthesis.addEventListener('voiceschanged', done, { once: true });
+		setTimeout(done, 1500);
+	});
+}
+
+const matches = (voice: SpeechSynthesisVoice, lang: string) =>
+	voice.lang.replace('_', '-').toLowerCase().startsWith(lang.slice(0, 2).toLowerCase());
+
+function best(list: SpeechSynthesisVoice[], lang: string) {
+	const candidates = list.filter((v) => matches(v, lang));
+	return (
+		candidates.find(
+			(v) => v.lang.replace('_', '-').toLowerCase() === lang.toLowerCase() && !v.localService
+		) ??
+		candidates.find((v) => v.lang.replace('_', '-').toLowerCase() === lang.toLowerCase()) ??
+		candidates[0]
+	);
+}
+
+export async function hasVoice(lang: string): Promise<boolean> {
+	return !!best(await voices(), lang);
+}
+
+export async function speak(text: string, lang: string, rate = 0.9) {
+	if (!supported()) return;
+	const voice = best(await voices(), lang);
+	speechSynthesis.cancel();
+	const utterance = new SpeechSynthesisUtterance(text);
+	utterance.lang = lang;
+	utterance.rate = rate;
+	if (voice) utterance.voice = voice;
+	speechSynthesis.speak(utterance);
+}