feat(slice-1): dev Postgres compose — single pinned service, named volume (D-7)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

compose.yaml

@@ -0,0 +1,26 @@
+# Dev datastore for ecomm — a single pinned PostgreSQL service (SD-0001 D-7).
+# The app runs natively (fast dev loop); only the database is containerized.
+# `scripts/dev.sh` owns this container's lifecycle. Reset to empty (to rehearse the
+# bootstrap, BUC-5) with:  docker compose down -v
+name: ecomm-dev
+
+services:
+  db:
+    # Pinned to the Cloud SQL major version ecomm targets in PPE/Prod (D-7).
+    image: postgres:16
+    environment:
+      POSTGRES_USER: ecomm
+      POSTGRES_PASSWORD: ecomm
+      POSTGRES_DB: ecomm
+    ports:
+      - "5432:5432"
+    volumes:
+      - ecomm-pgdata:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ecomm -d ecomm"]
+      interval: 2s
+      timeout: 3s
+      retries: 30
+
+volumes:
+  ecomm-pgdata: