feat(ADM-018): completed feature

work/artifacts/F-020/implementer.md

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+# Implementer — F-020 Shipping module
+
+## Summary
+Implemented server-side shipping quotation with zones, methods and free-shipping threshold behind `ShippingService.calculate(cartTotalCents, address)`.
+
+## Files changed
+- `project/migrations/015_shipping.js`
+- `project/src/modules/shipping/**`
+- `project/src/app/build-app.ts`
+- `project/src/app/tests/shipping.itest.ts`
+
+## Acceptance evidence
+- AC1 known zone: `shipping.itest.ts` seeds ES/28 zone with 500 cents method; `/shipping/calculate` returns 500.
+- AC2 unknown zone: same test sends US/94101 and gets HTTP 422 with `SHIPPING_ZONE_NOT_FOUND`.
+- AC3 free shipping threshold: same test sends cart total above threshold and gets 0/freeApplied.
+- `verify.sh`: passed.
+
+## Commands run
+- `cd project && npm run lint/typecheck/build/test` passed
+- `cd project && TEST_DATABASE_URL='postgres://mdv:mdv_dev_only@localhost:5432/mdv_test' npm run test:integration -- shipping.itest migrations.itest` passed; 12 files, 47 tests
+- `./scripts/verify.sh` passed
+
+## Notes
+- No new runtime dependency.
+- Carrier adapter remains an interface; no real carrier integration.
+- Cheapest active method per zone wins. Postal code prefix matching is most specific first.