Add repository artifact prune guard

[orenodinner]

/claim #10

Summary

• Adds repository-artifact-prune-guard/, a distinct Project Repository & Version Control slice for deciding whether stale or orphaned repository artifacts can be pruned before tagged release or export.
• Blocks deletion when artifacts are still bound to citation evidence, DOI version manifests, export bundle manifests, reproducibility packets, active retention holds, or minimum-age policy.
• Emits deterministic reviewer artifacts in JSON, Markdown, SVG, and MP4 form using synthetic data only.

Scope Boundaries

This is synthetic demo data only. It does not call Git providers, DOI services, storage APIs, access-control systems, credentials, or SCIBASE production services.

This scope is intentionally separate from existing #10 slices such as broad repository ledgers, component-owner approval, semantic tags, external reference pinning, notebook diffs, fork provenance, release signatures, restore rehearsal, compute sandboxes, retention/legal-hold, embargo release, or branch-protection drift guards.

Demo

• repository-artifact-prune-guard/reports/demo.mp4

Validation

• node repository-artifact-prune-guard/test.js
• node repository-artifact-prune-guard/demo.js
• git diff --check