feat(04-04): wire audio and speech into lesson, reward, forest, and app

- playCorrectSound() on correct keypress in letter and word exercises
- playRewardSound() when reward image appears
- speakText() for companion comment on reward screen
- playForestElementSound() when new forest element renders
- speakText() for companion greeting on forest screen

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ui/screens.ts

@@ -19,6 +19,7 @@ import { renderKeyboard, highlightKey, pressKey } from "../game/keyboard";
 import { getLevelByNumber } from "../game/levels";
 import { getLetterIntro } from "../companion/companion";
 import { getWordsForLevel } from "../game/words";
+import { playCorrectSound } from "../audio/sounds";
 
 export function initWelcomeScreen(
 	db: IDBDatabase,
@@ -213,6 +214,7 @@ export function initLessonScreen(
 
 			if (result.correct) {
 				cumulativeCorrect++;
+				playCorrectSound();
 				const currentEl = letterArea.querySelector(".falling-letter");
 				if (currentEl) {
 					currentEl.classList.add("falling-letter--dissolve");
@@ -288,6 +290,7 @@ export function initLessonScreen(
 
 			if (result.correct) {
 				cumulativeCorrect++;
+				playCorrectSound();
 
 				if (result.exerciseComplete) {
 					document.removeEventListener("keydown", onKeyDown);