feat(03-04): Dockerfile SSR multi-stage + docker-compose Traefik port 3000

- Rewrite Dockerfile: node:22-alpine build + runtime, copy .output/, node server
- Add .dockerignore excluding node_modules, .nuxt, .output, src, .git, .planning
- Update docker-compose loadbalancer port from 80 to 3000
- Add SMTP and GA4 environment variables to docker-compose

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -5,12 +5,17 @@ services:
     restart: unless-stopped
     environment:
       - TZ=Europe/Paris
+      - NUXT_SMTP_HOST=${NUXT_SMTP_HOST}
+      - NUXT_SMTP_USER=${NUXT_SMTP_USER}
+      - NUXT_SMTP_PASS=${NUXT_SMTP_PASS}
+      - NUXT_SMTP_TO=${NUXT_SMTP_TO}
+      - NUXT_PUBLIC_GTAG_ID=${NUXT_PUBLIC_GTAG_ID}
     networks:
       - public
     labels:
       - 'traefik.enable=true'
       - 'com.centurylinklabs.watchtower.enable=false'
-      - 'traefik.http.services.portfolio.loadbalancer.server.port=80'
+      - 'traefik.http.services.portfolio.loadbalancer.server.port=3000'
       # Main router (non-www)
       - 'traefik.http.routers.portfolio.rule=Host(`${PORTFOLIO_URL}`)'
       - 'traefik.http.routers.portfolio.entrypoints=websecure'