Add a multi-stage, uv-based Dockerfile producing a CPU image (with the
extract + spellcheck extras), plus a CUDA variant (Dockerfile.gpu) for
onnxruntime-gpu accelerated embeddings.
A single flexible entrypoint dispatches to the MCP stdio server (default)
or the mempalace CLI. All state -- palace, config, and the lazily
downloaded embedding model -- persists under /data via HOME, runs as a
non-root user, and is exposed as a volume.
Also add a docker-compose.yml for convenience, a GHCR publish workflow,
and a Docker section in the README.