compose: pass envs to backend

docker-compose.yaml

@@ -4,6 +4,11 @@ services:
       context: backend
       dockerfile: Dockerfile
     restart: always
+    environment:
+      - ROOT_PWD=${ROOT_PWD}
+      - DB_NAME=${DB_NAME}
+      - DB_SERVER=${DB_SERVER}
+      - DB_PORT=3306
     container_name: "${BACKEND_CT_NAME:-juhannus-invitation-backend}"
     depends_on:
       - db  # Ensure backend waits for db to start