Build .deb packages for amd64 and arm64 baselines

Parent: #123

Release pipeline produces `.deb` packages for `amd64` and `arm64` against the agreed distro baselines.

## Definition of done

- Baselines: Debian 12 (`bookworm`), Ubuntu 22.04 (`jammy`), Ubuntu 24.04 (`noble`).
- Architectures: `amd64` + `arm64`.
- One `.deb` per distro × arch combination (or one universal `.deb` if dependencies allow — decide during implementation; default to per-distro to avoid libc surprises).
- Built with `dotnet-deb` (Pkg.Tools.Cake-style) or `dpkg-deb` directly — decision recorded in the issue.
- Installs cleanly with `dpkg -i` on each baseline in a fresh container.
- `lintian` run on each `.deb`; warnings reviewed and either fixed or explicitly accepted (no expectation of zero warnings).