feat(docker): production-ready Dockerfile + Portainer compose stack

- Rewrite Dockerfile: multi-stage pnpm monorepo build with Next.js
  standalone output, non-root user, minimal runner image
- Enable next.config.ts `output: standalone` + serverExternalPackages
- Rewrite docker/compose.prod.yml: full production stack with migrate
  service, minio-init, named networks, build context for Portainer
- Add scripts/migrate.mjs: standalone Drizzle migration runner
- Update .dockerignore for cleaner build context

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

.dockerignore

@@ -1,15 +1,12 @@
 .git
-.gitignore
-README.md
-.env.local
-.env.*.local
+.github
 node_modules
-npm-debug.log
-coverage
-.turbo
-.next
-dist
+**/node_modules
+**/.next
+**/dist
+**/.turbo
+.env*
+!.env.example
+docker
+*.md
 .DS_Store
-.vscode
-.idea
-*.log