feat(quick-260329-ton): replace textContent with innerHTML + renderInlineMarkdown at all AI-text insertion points

- src/app.ts: greeting text now renders inline markdown
- src/ui/screens.ts: letter intro text now renders inline markdown
- src/forest/reward.ts: forest comment now renders inline markdown
- All 3 sites use innerHTML with XSS-safe renderInlineMarkdown

src/ui/screens.ts

@@ -20,6 +20,7 @@ import { getLevelByNumber } from "../game/levels";
 import { getLetterIntro } from "../companion/companion";
 import { getWordsForLevel } from "../game/words";
 import { playCorrectSound } from "../audio/sounds";
+import { renderInlineMarkdown } from "../utils/markdown";
 
 export function initWelcomeScreen(
 	db: IDBDatabase,
@@ -419,7 +420,7 @@ export function initLessonScreen(
 			if (cancelled) return;
 
 			// Show companion intro text
-			companionText.textContent = introText;
+			companionText.innerHTML = renderInlineMarkdown(introText);
 			companionArea.style.display = "flex";
 
 			// Show the letter