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/forest/scene.ts

@@ -1,6 +1,7 @@
 import type { Progress, LevelStatus } from "../types";
 import { levels } from "../game/levels";
 import { getProgress, getForestElements } from "../storage/db";
+import { playForestElementSound } from "../audio/sounds";
 
 let activeObjectUrls: string[] = [];
 
@@ -44,6 +45,7 @@ export async function renderForestScene(
 		// Animate newly added element
 		if (element.id === newElementId) {
 			slot.classList.add("forest__element--new");
+			playForestElementSound();
 		}
 
 		slot.appendChild(img);