Add challenge onboarding clock parity guard

[AlonePenguin]

Summary

• Adds a self-contained onboarding clock-start parity guard for issue Scientific Bounty System #18.
• Validates accepted-team starter workspace readiness before the submission clock starts: templates, starter-kit checksums, required tools, compute/storage quota baselines, support-channel visibility, setup-blocker timing, and extra privileged tool access.
• Includes synthetic clean/risky packets plus JSON, Markdown, SVG, and MP4 reviewer artifacts.

Non-overlap

This is an accepted-team onboarding/workspace readiness slice, separate from existing challenge intake, scoring/arbitration, prequalification, data-room access, escrow, payout routing/eligibility, appeals, duplicate-solver checks, scope-change control, sponsor compliance, and debrief feedback submissions.

Verification

• npm run check
• npm test
• npm run demo
• npm run verify-video
• git diff --check
• git diff --cached --check

/claim #18