Add private comment export guard

[yunrongy424-oss]

/claim #12

Adds a standalone collaborative private-comment export guard for the real-time collaborative research editor.

Private Comment Export Guard

• Checks public exports for private and reviewer-only comment threads
• Blocks unresolved threads when the export profile requires closure
• Flags mentions of reviewers outside the invited roster
• Holds sensitive inline annotations without redaction evidence
• Redacts emails and phone numbers from reviewer packets
• Emits deterministic JSON, Markdown, SVG, and MP4 demo artifacts

Demo And Validation

• Demo video: collaborative-private-comment-export-guard/reports/demo.mp4
• node collaborative-private-comment-export-guard/test.js -> passed
• node --check collaborative-private-comment-export-guard/index.js
• node --check collaborative-private-comment-export-guard/demo.js
• node --check collaborative-private-comment-export-guard/test.js
• node collaborative-private-comment-export-guard/demo.js -> generated JSON/Markdown/SVG reports
• python collaborative-private-comment-export-guard/make-demo-video.py -> generated demo MP4
• MP4 decode/read check returned a 720x1280 RGB frame
• Report spot checks found no synthetic email/phone leakage
• git diff --cached --check -> clean before commit

Synthetic data only. No private comments, reviewer identities, credentials, live editor services, payment rails, wallet data, or unrelated source changes are included.

[yunrongy424-oss]

Low-frequency bounty-claim follow-up.

The Algora claim page for this PR is still showing Pending / total paid $0: https://algora.io/claims/rWR9kPzbjKt34Ueg

The PR body includes the claim command and validation evidence; latest evidence includes: red/green validation passed, node checks passed, reports and demo MP4 were generated, and leakage/diff checks passed.

Is there any additional test output, demo evidence, or claim metadata needed from me before this can move into reward/payment review?