Added spanner emulator as DB

Makefile

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+.PHONY: up down down-volume logs ps
+
+up:
+	docker compose up -d spanner
+
+init:
+	docker compose up -d spanner-init
+
+down:
+	docker compose down
+
+down-volume:
+	docker compose down -v
+
+ps:
+	docker compose ps
+
+logs:
+	docker compose logs -f

ddl/schema.sql

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+CREATE TABLE item_stock (
+  id STRING(36) NOT NULL DEFAULT (GENERATE_UUID()),
+  name STRING(100),
+  amount INT64,
+  price NUMERIC,
+  sales_amount INT64
+) PRIMARY KEY (id);

docker-compose.yml

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+services:
+  spanner:
+    image: gcr.io/cloud-spanner-emulator/emulator:latest
+    container_name: spanner-emulator
+    ports:
+      - "9010:9010"   # gRPC
+      - "9020:9020"   # REST
+
+  spanner-init:
+    image: google/cloud-sdk:slim
+    container_name: spanner-init
+    depends_on:
+      - spanner
+    env_file:
+      - .env
+    environment:
+      # Tell gcloud/client libs to talk to the emulator inside the network
+      - SPANNER_EMULATOR_HOST=spanner:9010
+    volumes:
+      - ./scripts/spanner-init.sh:/work/spanner-init.sh:ro
+      - ./ddl:/work/ddl:ro
+    working_dir: /work
+    entrypoint: [ "bash", "/work/spanner-init.sh" ]

scripts/spanner-init.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+: "${SPANNER_PROJECT:?}"
+: "${SPANNER_INSTANCE:?}"
+: "${SPANNER_DATABASE:?}"
+
+# 1) Wait for emulator gRPC port (inside compose network it's "spanner:9010")
+for _ in $(seq 1 60); do
+  (echo >/dev/tcp/spanner/9010) >/dev/null 2>&1 && break
+  sleep 1
+done
+
+# 2) Point gcloud to the emulator (disable real IAM)
+export SPANNER_EMULATOR_HOST=spanner:9010
+gcloud config set auth/disable_credentials true >/dev/null
+gcloud config set core/project "${SPANNER_PROJECT}" >/dev/null
+gcloud config set api_endpoint_overrides/spanner http://spanner:9020/ >/dev/null
+
+# 3) Create instance & database (idempotent)
+gcloud spanner instances create "${SPANNER_INSTANCE}" \
+  --config=emulator-config --nodes=1 --description="Dev" >/dev/null 2>&1 || true
+
+gcloud spanner databases create "${SPANNER_DATABASE}" \
+  --instance="${SPANNER_INSTANCE}" >/dev/null 2>&1 || true
+
+# 4) Apply DDL
+gcloud spanner databases ddl update "${SPANNER_DATABASE}" \
+  --instance="${SPANNER_INSTANCE}" \
+  --ddl-file="/work/ddl/schema.sql" >/dev/null