docs: correct release process to match deployed Prow config

[aevyrie]

The previous ## Release Process section described a draft-release postsubmit on push to main producing a v{version}-tagged draft. That job is not deployed. The actual publish trigger in fslabs-infra (modules/ci/prow/terragrunt.hcl) is a publish-all postsubmit on branches matching ^cargo-fslabscli-\d+\.\d+\.\d+$, which runs fslabscli publish and creates the tag as cargo-fslabscli-{version}.

This PR rewrites the section (steps + Mermaid diagram) so it matches what actually runs.

[fslabs-bot]

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