chore: dockerize Next.js app (multi-stage build, standalone output)

- Dockerfile: 3-stage build (deps → builder → runner) using node:20-alpine
- .dockerignore: excludes node_modules, .next, secrets, graphify-out
- docker-compose.yml: runtime secrets via env, build-time NEXT_PUBLIC_* via args
- Render worker service pre-wired (commented out, opt-in)

Dockerfile

@@ -0,0 +1,62 @@
+# ── Stage 1: install dependencies ────────────────────────────────────────────
+FROM node:20-alpine AS deps
+RUN apk add --no-cache libc6-compat
+WORKDIR /app
+
+COPY package.json package-lock.json* ./
+RUN npm ci
+
+# ── Stage 2: build ───────────────────────────────────────────────────────────
+FROM node:20-alpine AS builder
+WORKDIR /app
+
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+# NEXT_PUBLIC_* vars are embedded at build time — pass them as build args.
+# Server-side secrets (STRIPE_SECRET_KEY, SUPABASE_SERVICE_ROLE_KEY, etc.)
+# are injected at runtime via env / docker-compose and never baked into the image.
+ARG NEXT_PUBLIC_SUPABASE_URL
+ARG NEXT_PUBLIC_SUPABASE_ANON_KEY
+ARG NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY
+ARG NEXT_PUBLIC_SITE_URL=http://localhost:3000
+
+ENV NEXT_PUBLIC_SUPABASE_URL=$NEXT_PUBLIC_SUPABASE_URL
+ENV NEXT_PUBLIC_SUPABASE_ANON_KEY=$NEXT_PUBLIC_SUPABASE_ANON_KEY
+ENV NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=$NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY
+ENV NEXT_PUBLIC_SITE_URL=$NEXT_PUBLIC_SITE_URL
+
+ENV NEXT_TELEMETRY_DISABLED=1
+ENV NODE_ENV=production
+
+RUN npm run build
+
+# ── Stage 3: production runner ────────────────────────────────────────────────
+FROM node:20-alpine AS runner
+WORKDIR /app
+
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
+
+# Create a non-root user (security best practice)
+RUN addgroup --system --gid 1001 nodejs \
+ && adduser  --system --uid 1001 nextjs
+
+# Copy public assets
+COPY --from=builder /app/public ./public
+
+# standalone output: server.js + chunk bundles (no full node_modules)
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static     ./.next/static
+
+# Prepare prerender cache dir with correct ownership
+RUN mkdir -p .next && chown nextjs:nodejs .next
+
+USER nextjs
+
+EXPOSE 3000
+ENV PORT=3000
+ENV HOSTNAME=0.0.0.0
+
+# Next.js standalone entry point
+CMD ["node", "server.js"]