Add Docker/Traefik deployment setup

Dockerfile

@@ -0,0 +1,30 @@
+# syntax=docker/dockerfile:1
+
+FROM node:20-alpine AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci
+
+FROM node:20-alpine AS builder
+WORKDIR /app
+# The /plans/[code] route uses generateStaticParams + dynamicParams = false,
+# so PLANS_PAGES must be known at build time — codes not baked in here will
+# 404 at runtime no matter what PLANS_PAGES is set to when the container runs.
+ARG PLANS_PAGES
+ENV PLANS_PAGES=$PLANS_PAGES
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+RUN npm run build
+
+FROM node:20-alpine AS runner
+WORKDIR /app
+ENV NODE_ENV=production
+ENV PORT=3000
+ENV HOSTNAME=0.0.0.0
+
+COPY --from=builder /app/public ./public
+COPY --from=builder /app/.next/standalone ./
+COPY --from=builder /app/.next/static ./.next/static
+
+EXPOSE 3000
+CMD ["node", "server.js"]