Debian GUI upgrade helper (release notification + deb822 sources rewrite + postpone option)

No repository files, tests, or entry points are named. Start by mapping the existing Update Manager GUI and its PackageKit/apt integration, then define the release-detection, postpone, source-backup and deb822-rewrite flow. Done means a guided Debian stable upgrade with safety checks, progress reporting, and a restore path.

Is your feature request related to a problem? Please describe.
I support users who are not comfortable with the shell and know also some people, who'd like to install Linux, but aren't familiar with the terminal. Keeping their laptops up-to-date especially if there is a new Debian version is a bit tedious, because sometimes they moved away etc and then I think, that after a while they'd wonder about the old software and why it's not updating.

Describe the solution you'd like
A simple, guided UI would dramatically reduce support load and mistakes. Debian has the pieces (PackageKit/Discover/GNOME updater), but a small glue tool would make upgrades approachable. So I'm looking for a small Debian‑friendly GUI that:

• notifies when a new Debian stable is available (e.g., bookworm → trixie),
• lets the user Upgrade now or Postpone,
• safely rewrites APT sources to deb822 (backup first, handle Signed‑By, respect pinning/backports), preferably using “apt modernize-sources,”
• then runs a standard PackageKit/apt full upgrade and shows progress.

Describe alternatives you've considered
Meeting the people in person to change the sources.list entries on my own.

Additional context
Possible UX specs:

• Detect new stable:
  • Check Debian release info (announce feed or Release Notes URL), or compare current /etc/os-release codename with “stable” suite via APT policy. Show banner: “Debian 13 ‘trixie’ is available.”
  • Offer: “Upgrade now”, “Remind me later (in 1/7/30 days)”, “Skip this release”.
• Prepare sources (with deb822):
  • Run apt modernize-sources; back up /etc/apt/sources.list* and .list files; consolidate into /etc/apt/sources.list.d/debian.sources; switch suites bookworm→trixie (or stable), keep components, adjust backports, unpin APT if needed; preserve third‑party entries and warn if incompatible.
• Upgrade flow:
  • Trigger the user’s existing GUI (gnome-package-updater or Discover) with PackageKit, show logs, and reboot prompt.
• Safety rails:
  • Timeshift/snapshot reminder, disk space check, network check, “dry run” simulation, and a “restore sources from backup” button.