DB를 MySQL에서 PostgreSQL로 전면 전환

- Sequelize dialect를 postgres로 변경, mysql2 대신 pg/pg-hstore 사용
- docker-compose: postgres:16-alpine + pg_isready healthcheck, 호스트 포트 5442
- 환경변수 MYSQL_PORT -> DB_PORT로 통일, .env.example 갱신

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.yml

@@ -1,19 +1,20 @@
 services:
-  mysql:
-    image: mysql:8.0
+  postgres:
+    image: postgres:16-alpine
     container_name: report-db
     restart: always
     environment:
-      MYSQL_DATABASE: ${DB_NAME:-report_db}
-      MYSQL_ROOT_PASSWORD: ${DB_PASSWORD:-daoblock12!!}
+      POSTGRES_DB: ${DB_NAME:-report_db}
+      POSTGRES_USER: ${DB_USER:-postgres}
+      POSTGRES_PASSWORD: ${DB_PASSWORD:-daoblock12!!}
     ports:
-      - "3316:3306"
+      - "5442:5432"
     volumes:
-      - mysql-data:/var/lib/mysql
+      - postgres-data:/var/lib/postgresql/data
     networks:
       - report-network
     healthcheck:
-      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1"]
+      test: ["CMD-SHELL", "pg_isready -U ${DB_USER:-postgres} -d ${DB_NAME:-report_db}"]
       interval: 5s
       timeout: 5s
       retries: 20
@@ -26,8 +27,9 @@ services:
     ports:
       - "${BACKEND_PORT:-54530}:3000"
     environment:
-      - DB_HOST=${DB_HOST:-mysql}
-      - DB_USER=${DB_USER:-root}
+      - DB_HOST=${DB_HOST:-postgres}
+      - DB_PORT=${DB_PORT:-5432}
+      - DB_USER=${DB_USER:-postgres}
       - DB_PASSWORD=${DB_PASSWORD:-daoblock12!!}
       - DB_NAME=${DB_NAME:-report_db}
       - ACCESS_SECRET=${ACCESS_SECRET:-your_jwt_access_secret_123}
@@ -36,7 +38,7 @@ services:
       - ADMIN_PASS=${ADMIN_PASS:-kyeongmi}
       - JEMINI_KEY=${JEMINI_KEY}
     depends_on:
-      mysql:
+      postgres:
         condition: service_healthy
     volumes:
       - ./backend/img:/app/img
@@ -59,4 +61,4 @@ networks:
     driver: bridge
 
 volumes:
-  mysql-data:
+  postgres-data: