[httpsphl]

Closes the other Linux gap (spec 15.4): removing the .deb now stops Botloft's background service, as the NSIS uninstall hook does on Windows.

• app/src-tauri/linux/prerm.sh is wired as the .deb's preRemoveScript. dpkg runs it as root; it acts only on remove or purge. The in-app updater installs a new .deb, which calls it with upgrade, and that leaves everything alone.
• For each ~/.config/systemd/user/botloft.service in /home/* and /root:
  • If the user's manager is up, it runs botloftd --home ~/.local/share/Botloft service uninstall as that user (runuser, with HOME, XDG_RUNTIME_DIR and their session bus).
  • Either way, it removes the unit, its default.target.wants link and ~/.config/autostart/botloft.desktop, which covers users who are signed out.
  • Bots and data stay.
• The AppImage and the macOS app have no uninstaller; the docs keep the manual step for them.
• The README and the code signing policy describe 0.8.0, so they change with the next release.

Tests

• Debian container, as root, with two made-up users and a fake botloftd that records its call:
  • upgrade changes nothing.
  • remove calls ana's daemon as ana, with her home, runtime dir and data folder; bob has no session and only loses the files.
  • No service or sign-in file is left, and the data stays.
• Release dry run (run 36954348480): the built .deb carries prerm, mode 0755.

Manual test (not done yet)

On Ubuntu: install the .deb, open Botloft, then sudo apt remove botloft. systemctl --user status botloft should no longer find the unit, and no botloftd should run.