Add challenge IP redaction gate

[2bf]

Summary

/claim #18

Adds a self-contained challenge-ip-redaction-gate module for the Scientific Bounty System. The slice protects solver-owned IP during sponsor review by redacting protected artifacts before funded settlement, allowing NDA-cleared reviewer packets, and producing deterministic audit digests for arbitration evidence.

Included

• Dependency-free disclosure policy engine in challenge-ip-redaction-gate/index.js
• Synthetic sponsor/reviewer/settlement demo in challenge-ip-redaction-gate/demo.js
• Regression tests in challenge-ip-redaction-gate/test.js
• Requirement map and run instructions in challenge-ip-redaction-gate/README.md
• Short demo artifact: challenge-ip-redaction-gate/demo.mp4

Validation

• node challenge-ip-redaction-gate/test.js -> 6 tests passed
• node challenge-ip-redaction-gate/demo.js -> emits sponsor redaction, reviewer packet, and funded-settlement unlock examples
• ffprobe -v error -show_entries format=duration,size -show_entries stream=width,height,codec_name -of default=noprint_wrappers=1 challenge-ip-redaction-gate/demo.mp4 -> h264, 1280x720, 5 seconds
• git diff --cached --check passed before commit

AI-assisted with OpenAI Codex; I reviewed and verified the diff locally.