feat: Docker production setup (Portainer + Traefik)

Adds multi-stage Dockerfile (runner + worker targets), docker-compose.prod.yml
with Traefik labels, auto-migration on deploy, and next.config.ts standalone
output mode.

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

next.config.ts

@@ -4,6 +4,7 @@ import createNextIntlPlugin from 'next-intl/plugin';
 const withNextIntl = createNextIntlPlugin('./src/i18n/request.ts');
 
 const nextConfig: NextConfig = {
+  output: 'standalone',
   serverExternalPackages: ['@react-pdf/renderer'],
 };