Add release binaries, Golang CI, Docker images

[khvn26]

We need to establish a build workflow for the new CLI, and connect it to GitHub releases.

Acceptance criteria

• pre-commit runs Go linting (locally and in CI) and CI runs tests.
• This repo has a release-please configuration checked in, and release-please check is running without errors against main.
• A release triggers CLI binaries builds for all viable platforms/architectures. They are attached to the GitHub release.
• A release triggers a Docker build. The multi-arch Docker images are tagged with release tags, :latest, and published to ghcr.io. Optionally, a main push triggers a :main Docker tag publish.