- Generalize _read_md_cached() for generic file caching
- Add find_sub_home_for_lesson() and get_sub_home_data() helpers
- Add /api/bab/<folder> endpoint
- Detect sub-home in api_lesson for nav context
- Skip sub-home.md in find_lesson_file() and _parse_lesson_links()
- Add title to bab frontend page data
- Update generate_tokens.py & content_parser.py to skip sub-home.md