fix: I dunno, I'm making git server changes

backend/Dockerfile

@@ -1,7 +1,11 @@
 # Production Dockerfile for MotoVaultPro Backend
+# Uses mirrored base images from GitLab Container Registry
+
+# Build argument for registry (defaults to GitLab mirrors, falls back to Docker Hub)
+ARG REGISTRY_MIRRORS=registry.motovaultpro.com/mirrors
 
 # Stage 1: Build stage
-FROM node:lts-alpine AS builder
+FROM ${REGISTRY_MIRRORS}/node:20-alpine AS builder
 
 # Install build dependencies
 RUN apk add --no-cache dumb-init git curl
@@ -27,7 +31,7 @@ ENV DOCKER_BUILD=true
 RUN npm run build
 
 # Stage 2: Production runtime
-FROM node:lts-alpine AS production
+FROM ${REGISTRY_MIRRORS}/node:20-alpine AS production
 
 # Install runtime dependencies only (postgresql-client for backup/restore)
 RUN apk add --no-cache dumb-init curl postgresql-client