Debian/Ubuntu packaging: offer to contribute debian/ directory for .deb builds

Is your feature request related to a problem? Please describe.

auto-cpufreq has excellent packaging for Snap, Nix, AUR, Gentoo, OpenRC, runit, s6, and dinit — but not for Debian/Ubuntu via .deb packages. Users on Debian-based distros currently rely on the installer script (creates a venv in /opt/) or the Snap package (limited: no GUI, confinement issues).

The existing request #157 (2020) asked for this but it was never implemented.

Describe the solution you'd like

A minimal debian/ directory that produces a proper .deb package. The approach is surgical:

1. A self-contained debian/ directory (zero changes to existing code)
2. Uses dh_virtualenv to keep the existing venv isolation (no need to port from Poetry to setuptools)
3. Installs the systemd service to the standard /lib/systemd/system/ path
4. Handles polkit policy, desktop file, and icon via debhelper
5. Existing installer + Snap continue working unchanged — the .deb is purely additive

I'm willing to create a PR for this. Would that be welcome?

Describe alternatives you've considered

• Snap package already exists but has confinement issues (no GUI, no battery threshold control)
• Installer script works but doesn't integrate with dpkg/apt (no dependency resolution, no clean removal tracking)
• Asking a Debian maintainer to package it upstream would take longer

Additional context

I use this tool on multiple Debian machines and having a .deb would make deployment and updates much smoother. Happy to maintain the packaging going forward.