Add negative evidence graph guard

[shaiananvari8]

summary
adds knowledge graph negative evidence guard for scibase issue #17.
holds public graph recommendations that depend on retractions unresolved contradictions failed replications stale negative evidence reviews or private evidence.
adds reviewer reports and demo transcript evidence under knowledge graph negative evidence guard reports.

verification
npm run check passed.
npm test passed 6 tests.
npm run demo produced status block publication and digest b245bc907bb0911addeb552f2bd24ed4c51e6f895cceca6840a3985df1af39ac.

safety
synthetic graph packets only. no credentials private research data external apis ontology calls storage writes or live project mutations.

/claim #17

[shaiananvari8]

/claim #17

Validation note for this PR:

• Scope: knowledge-graph-negative-evidence-guard for SCIBASE issue Scientific Knowledge Graph Integration #17.
• Evidence: synthetic reviewer packet, Markdown report, and SVG summary under knowledge-graph-negative-evidence-guard/reports/.
• Local checks: npm run check, npm test, npm run demo.
• Safety: synthetic graph packets only; no credentials, private research data, external APIs, ontology calls, storage writes, or live project mutations.