Refactor PostgreSQL environment variables in docker-compose.yaml to use variable substitution for improved configuration management.

docker-compose.yaml

@@ -55,8 +55,8 @@ services:
       - backend
     environment:
       DEBUG: true
-      POSTGRES_DB: phoenix
-      POSTGRES_PASSWORD: "8*6&Ti3TJxN^"
+      POSTGRES_DB: ${DB_NAME}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
     volumes:
       - "./database:/var/lib/postgresql/data"
     # deploy: