[Booshdag-io]

Closes #43

Summary

Addresses challenge and ghost replay desynchronization caused by passage list changes:

• Adds passage th (short textHash of the initial passage) into challengePayload().
• Updates CHALLENGE_VERSION to 2 while maintaining backwards compatibility for version 1 payload decoding.
• Detects passage drift on load to prevent unfair win/loss verdicts against mismatched ghosts.

[TMHSDigital]

Thanks for picking up #43. This PR can't be merged as it stands: challengePayload() calls firstPassageText, which doesn't exist, so building any challenge link throws a ReferenceError. Also, parseChallenge still accepts only CHALLENGE_VERSION, so raising it to 2 would have rejected every existing link. #43 is now done in 1ebcae1, using the hash idea from this PR. It adds the check when a link is opened, the warning, the same handling for Ghost Mode bests, and tests. Closing as replaced by that commit.