XY-929: Expand graph/RAG adapters beyond scored smokes

[yvette-carlisle]

Summary

• add representative graph/RAG external-adapter fixtures for RAGFlow, LightRAG, GraphRAG, Graphiti/Zep, and graphify
• add a dedicated benchmark task plus manifest/report updates that preserve smoke-only, blocked, incomplete, and wrong_result claim boundaries
• refresh adoption/report docs and JSON evidence so broad graph/RAG quality claims remain typed rather than overclaimed

Validation

• git diff --check
• cargo make fmt
• cargo make lint-fix
• cargo make checks

Notes

• Decodex attempt xy-929-attempt-1-1781215003 reached validation-ready with repo gate passing, then stopped before commit/PR handoff; this PR is a manual reconciliation of that retained worktree.
• XY-930 remains blocked until private corpus or credentialed provider inputs exist.