feat(05-01): extend Progress type with currentForestPage, add paginated renderForestScene

- Add currentForestPage: number field to Progress interface in types.ts
- Export SLOTS_PER_PAGE = 12 constant from scene.ts
- Change renderForestScene signature to accept page: number parameter
- Slice elements by page (start/end = page * SLOTS_PER_PAGE)
- Update navigation UI (forest-nav) after rendering
- Add migrateProgress entry for currentForestPage in app.ts
- Fix Progress object literals in db.test.ts and screens.ts to include new field

src/types.ts

@@ -18,6 +18,7 @@ export interface Progress {
 	totalErrors: number;
 	errorKeyCounts: Record<string, number>;
 	lastPlayedLevels: number[]; // last 3 played levels for review mechanic
+	currentForestPage: number; // 0-indexed, default 0
 }
 
 export type LessonPhase = "discover" | "practice" | "words";