feat(T06): deployment config - Dockerfiles, docker-compose, Coolify guide, env example

frontend/Dockerfile

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+# ERP Nutzfahrzeuge — Frontend Dockerfile
+# Node 18 + Next.js 14.2.5 standalone build
+# Multi-stage build: deps -> builder -> runner
+
+# ============ Stage 1: Dependencies ============
+FROM node:18-alpine AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci
+
+# ============ Stage 2: Build ============
+FROM node:18-alpine AS builder
+WORKDIR /app
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+# Build-time environment variables
+ARG NEXT_PUBLIC_API_URL=http://localhost:8000/api/v1
+ENV NEXT_PUBLIC_API_URL=$NEXT_PUBLIC_API_URL
+
+RUN npm run build
+
+# ============ Stage 3: Runner (production) ============
+FROM node:18-alpine AS runner
+WORKDIR /app
+
+ENV NODE_ENV=production
+
+# Non-root user for security
+RUN addgroup --system --gid 1001 nodejs && \
+    adduser --system --uid 1001 nextjs
+
+# Copy standalone build output
+COPY --from=builder /app/public ./public
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
+
+USER nextjs
+
+EXPOSE 3000
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 --start-period=10s \
+    CMD wget --no-verbose --tries=1 --spider http://localhost:3000/ || exit 1
+
+CMD ["node", "server.js"]