Publish xudanu-server to crates.io

[jonesd]

Goal

Allow users to install with:

cargo install xudanu-server --features server

Steps

1. Add crates.io metadata to Cargo.toml (description, repository, license, readme, keywords, categories)
2. Create crates.io account and API token
3. Test with cargo publish --dry-run
4. Publish with cargo publish
5. Optionally set up CI auto-publish on tag push

Also publish a Docker image to GitHub Container Registry for container deployment.

Context

Previously tracked in TODO.md (v0.1.2 item). Xudanu is at v0.9.0 and ready for wider distribution.