Add in-file rationale documentation for disabled semver-checks and publish in release-plz.toml

## Objective
In `release-plz.toml`, `semver_check = false` and `publish = false` are currently set without in-file documentation. While justified (this is a standalone binary crate, not a published library crate on crates.io, so `cargo-semver-checks` has no public API library contract to validate), adding explicit in-file comments ensures future maintainers understand the architectural rationale and tradeoffs.

## Tasks
- [ ] Add explicit header comments to `release-plz.toml` explaining:
- Why `semver_check = false` is set (binary crate with no public library API contract).
- Why `publish = false` is set (crate is published via Docker images / GitHub releases, not crates.io).
- [ ] Confirm no orphaned workflow files reference deleted semver-check actions.

## Acceptance Criteria
- [ ] `release-plz.toml` contains clear, maintainable inline documentation explaining both settings.