Add knowledge graph recommendation diversity guard

[vultuk]

@algora-pbc /claim #17

Summary

• Adds knowledge-graph-recommendation-diversity-guard, a focused Scientific Knowledge Graph Integration slice for issue Scientific Knowledge Graph Integration #17.
• Validates discovery-mode recommendation sets before researchers see them.
• Checks institution, funder, domain, and method concentration; citation-herd risk; stale evidence dominance; and missing recommendation rationale paths.
• Keeps safe recommendations visible while holding biased or brittle sets for curator action.
• Emits reviewer artifacts: JSON audit packet, Markdown report, SVG summary, and a 12-second MP4 walkthrough.

Validation

• node knowledge-graph-recommendation-diversity-guard/test.js -> 5 knowledge graph recommendation diversity guard tests passed
• node knowledge-graph-recommendation-diversity-guard/demo.js -> status=hold, showable=2/5, blockers=9, warnings=3, staleEvidenceShare=0.6
• node --check knowledge-graph-recommendation-diversity-guard/index.js
• node --check knowledge-graph-recommendation-diversity-guard/sample-data.js
• node --check knowledge-graph-recommendation-diversity-guard/test.js
• node --check knowledge-graph-recommendation-diversity-guard/demo.js
• git diff --check

The demo status is intentionally hold: it demonstrates the guard catching a recommendation set dominated by one institution/funder/method cluster, stale evidence, and thin rationale paths before discovery-mode publication.

BTC payout address for this bounty goal: bc1qa5acxqc3wldzxwjhe8a65gjp6n7dxmafm6qs4j