Phase 0 foundation: canonical schema, ingest pipeline, CRM MCP server

Workstream A–C substrate for the Ten31 agentic system:
- A1: docs/crm-overview.md; CLAUDE.md conventions + guardrail #9
- A2: additive/reversible core migration (canonical_entities, entity_links,
  interaction_log, relationship_edges, soft-delete) + ledgered runner
- B1/B3: chunking + deterministic entity resolution (backend/ingest)
- B2: dense (bge-m3) + BM25 sparse ingest to Qdrant crm_chunks
- C: CRM MCP server (reads, retrieval modes, logged writes) — no outbound tools
- docs: redaction/re-hydration, Gmail enablement runbook
- synthetic test data; .env.example; housekeeping (.gitignore, untrack crm.db,
  drop legacy files + start9/0.3.5)

Verified end-to-end on synthetic data + live Sparks (hybrid > dense on entity
queries). Real backfill runs on Ten31 infra; index holds synthetic data only.
Branch snapshot also captures pre-existing working-tree changes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/email_integration/__init__.py

@@ -0,0 +1,15 @@
+"""
+Gmail Integration for Venture CRM.
+
+Phase 1 scope: OAuth2/DWD authentication, incremental Gmail sync, MIME parsing,
+investor matching, threading, attachment storage. All logic isolated to this
+module; server.py integration is a 3-line patch guarded by
+CRM_GMAIL_INTEGRATION_ENABLED.
+
+See GMAIL_INTEGRATION_ARCHITECTURE.md at the repo root for full design.
+"""
+
+from . import config  # noqa: F401
+from . import errors  # noqa: F401
+
+__all__ = ["config", "errors"]