feat(04-01): add audio/speech modules and speechEnabled to Settings

- Create src/audio/sounds.ts with playCorrectSound, playRewardSound, playForestElementSound
- Create src/audio/speech.ts with speakText via Web Speech API
- Add speechEnabled field to Settings interface in types.ts
- Add speechEnabled defaults in all Settings initializers (gemini.ts, parent.ts, db.test.ts)
- All sound functions check audioEnabled, speakText checks speechEnabled
- AudioContext lazy initialization for autoplay policy compliance

src/api/gemini.ts

@@ -125,6 +125,7 @@ function getDefaultSettings(): Settings {
 	return {
 		id: 1,
 		audioEnabled: true,
+		speechEnabled: false,
 		apiKey: "",
 		apiCallsToday: { text: 0, image: 0 },
 		lastApiCallDate: getTodayDate(),