Alpine crond doesn't inherit the container environment, so
OUTLINE_API_TOKEN and other vars were missing. Dump env at
startup and source it in each cron entry.
- Add cron service to docker-compose with backup (3 AM) and export (4 AM) schedules
- Remove redundant content/articles/ and content/curriculum/ (now in Outline, exported to content/wiki/)
- Fix env var mismatch: support both OUTLINE_API_KEY and OUTLINE_API_TOKEN
- Drop updatedAt from export frontmatter to reduce noisy commits
- Add backups/ to gitignore
