Adds a multi-stage Dockerfile and .dockerignore and updates Next.js config to produce a standalone production build.
Enables reproducible, smaller production images by leveraging Next's standalone/output tracing, creating a non-root runtime user, and copying only required static and server files. Supports yarn, npm, and pnpm lockfile-driven installs, installs minimal Alpine packages for compatibility and healthchecks, and exposes a production port for containerized deployment.
