feat(ctf): export the curriculum to CTFd / RootTheBox format #317

Context

Depends on the per-instance flag decision #316. An export from challenges.json lets organisers drop the lab into an existing scoreboard and redistribute to dozens of players — a strong organic-adoption lever.

Tasks

• Generate a CTFd-compatible export (and/or RootTheBox) from the roadmap/challenges.json.
• Wire flags to the per-instance mechanism.
• Document the import flow.

Acceptance criteria

• The export imports cleanly into a fresh CTFd instance with correct categories, difficulty, hints.

Files

• scripts/, docs/