Add challenge evidence freeze gate

[IOROHKI]

/claim #18

Summary

• Adds a focused challenge evidence freeze and tamper-diff gate for SCIBASE issue Scientific Bounty System #18.
• Freezes solver submission manifests at the challenge deadline, compares post-deadline sponsor/reviewer packets against the frozen manifest, and flags checksum drift, metric drift, late-added primary artifacts, removals, metadata drift, and missing reviewer-visible exception justifications.
• Produces scoring exclusions, arbitration/payout hold decisions, reviewer tasks, public exception notes, deterministic audit packets, JSON/Markdown/SVG outputs, and a short MP4 demo artifact.

@algora-pbc /claim #18

Demo

• Short demo video: challenge-evidence-freeze-gate/reports/demo.mp4
• SVG preview: challenge-evidence-freeze-gate/reports/freeze-gate.svg
• Audit packet: challenge-evidence-freeze-gate/reports/freeze-audit.json

Validation

• node challenge-evidence-freeze-gate/test.js
• node challenge-evidence-freeze-gate/demo.js
• node --check challenge-evidence-freeze-gate/index.js
• node --check challenge-evidence-freeze-gate/sample-data.js
• node --check challenge-evidence-freeze-gate/demo.js
• node --check challenge-evidence-freeze-gate/test.js
• git diff --check
• MP4 verification: imageio-ffmpeg decoded challenge-evidence-freeze-gate/reports/demo.mp4 without errors

Notes

• Synthetic data only.
• No credentials, network calls, or external runtime dependencies in the module.
• This slice is distinct from intake, arbitration/scoring, appeals, workspace privacy, anti-collusion, escrow settlement, payout eligibility, sponsor reliability, reviewer consensus, IP redaction, amendment-control, reproducibility audit, and milestone-progress modules.

[IOROHKI]

@algora-pbc /claim #18