Add Docker support with multi-stage build

Enable output: standalone in next.config.ts so Next.js produces a
self-contained server bundle in .next/standalone. Multi-stage Dockerfile
(deps -> builder -> runner) on node:20-alpine keeps the final image
minimal; app runs as a non-root user for security. .dockerignore
excludes node_modules, .next, .env files, and editor tooling.

To build and run:
  docker build -t portfolio .
  docker run -p 3000:3000 portfolio

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,43 @@
+# syntax=docker/dockerfile:1
+
+# ── 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 the app ────────────────────────────────────────────────────
+FROM node:20-alpine AS builder
+WORKDIR /app
+
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+RUN npm run build
+
+# ── Stage 3: production runner ────────────────────────────────────────────────
+FROM node:20-alpine AS runner
+WORKDIR /app
+
+ENV NODE_ENV=production
+ENV PORT=3000
+ENV HOSTNAME="0.0.0.0"
+
+# Run as non-root for security
+RUN addgroup --system --gid 1001 nodejs \
+ && adduser  --system --uid 1001 nextjs
+
+# Static assets
+COPY --from=builder /app/public ./public
+
+# Standalone server + compiled output (standalone mode bundles only what's needed)
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static   ./.next/static
+
+USER nextjs
+
+EXPOSE 3000
+
+CMD ["node", "server.js"]