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/types.ts

@@ -53,6 +53,7 @@ export interface ForestElement {
 export interface Settings {
 	id: 1; // singleton
 	audioEnabled: boolean;
+	speechEnabled: boolean;
 	apiKey: string;
 	apiCallsToday: { text: number; image: number };
 	lastApiCallDate: string; // ISO date "YYYY-MM-DD"