Transform+load: unified customer master (migration step 3, customers)

migration/transform_customers.py builds `customers` + `customer_legacy_refs`
from staged DATGRAL, implementing the reconciliation rules: utilities DATGRAL
is the customer master; insurance DATGRAL folds in via its num_util
cross-reference (matches enrich the master with the ID-document fields
utilities lacks); COBRO3 excluded as a charge batch. Every legacy row gets a
provenance ref, so the load is auditable and idempotent (truncate+rebuild).

Loaded and validated against the dev DB (192.168.4.212:3307):
  1682 customers (1172 utilities master + 510 insurance-only)
  2242 legacy refs (1172 utilities + 1070 insurance) — 0 orphans
  560 insurance rows linked via num_util, 0 broken cross-refs
  542 merged identities spanning both business lines
Spot-checked a merged customer: single record carrying utilities fee +
insurance passport/ID enriched in, both provenance refs present.

RESUME.md: mark customers done, record dev-DB infra + the pnpm/npm caveat.

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

.gitignore

@@ -12,3 +12,6 @@ __pycache__/
 *.pyc
 packages/database/generated/
 .DS_Store
+
+# local package-manager shim (machine npm is pnpm-aliased); npm is canonical
+pnpm-lock.yaml