automate node version

Dockerfile.backend

@@ -1,14 +1,14 @@
-# ---- Build stage ----
-FROM node:22-alpine AS builder
+ARG NODE_VERSION=25-alpine
+FROM node:${NODE_VERSION} AS builder
 WORKDIR /app
 COPY server/package.json server/package-lock.json* ./
-RUN npm install && npm audit fix
+RUN npm install
 COPY server/src ./src
 COPY server/tsconfig.json ./
 RUN npm run build
 
 # ---- Runtime stage ----
-FROM node:22-alpine
+FROM node:${NODE_VERSION}
 WORKDIR /app
 COPY --from=builder /app/dist ./dist
 # schema.sql is read by the migrate script at runtime