Publish OCI image

[aj-stein]

Committer Notes

Closes #561.

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Summary by CodeRabbit

• Chores

  • Added automated container build-and-publish CI with optional push, cross-platform images (amd64/arm64), image metadata/tags and attestations; CI now uploads built CLI artifact and runs a container build job to produce minimal non-root CLI images for CI and local use.

• Documentation

  • Added "Installing the CLI tool" guide covering building from source, pre-built snapshots/releases, and running the CLI via container images.

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