session and seat management

The current documentation for session and seat management is pretty neutral and doesn't suggest any solution. It provides 4 sections with different options, where the user has to basically always choose dbus and then one or two other options, of which some overlap or conflict.

I think the core issues that should be addressed are:

1. dbus session bus: turnstile
2. XDG_RUNTIME_DIR: turnstile or elogind
3. user services for pipewire, pipewire-pulse and wireplumber: turnstile
4. Wayland: elogind or seatd
5. polkit, rtkit: elogind
6. power management (hooks, events and triggering (swayidle, gnome, kde)): elogind

If we want to solve them that makes turnstile a hard requirement, no more hacky dbus-run-session, no more xdg autostart bullshit for user services.

Then the next choice is between elogind and seatd, seatd only provides the bare minimum to make wayland work. elogind solves the core issues and provides additional features like uaccess udev device access and the logind dbus api for desktop environments.

Might also make sense to just make this default for the desktop ISOs.

まず、現在の session と seat の管理に関するドキュメントと、その 4 つのオプションセクションを確認します。各オプションが提供するコンポーネントを整理し、そのうえで、推奨される組み合わせ、トレードオフ、および Desktop ISO のデフォルト候補が明確になるようにガイダンスを再構成します。ユーザーが記載されているハックに頼らずに動作するセットアップを選択できれば完了です。