[HANDOFF] D1 Citation Graph Database — Structured Data Foundation

**Priority:** 🔴 P0 | **Sessions:** 1 | **Phase:** 3

**Handoff file:** riefings/handoffs/d1-citation-graph-2026-05-28.md

**Scope:** 4-table D1 schema (papers, citations, concepts, paper_concepts). Seed from 9 published papers. Foundation for Concept Graph, Cross-Paper Consistency Engine, Evidence Deck.

**Status:** ⬜ READY — Awaiting Projects Agent pickup