[Feature] Create PPA for Ubuntu

[veritas5]

It would be more convenient for Ubuntu users if a PPA was created instead of having to install from a standalone DEB. Makes staying up to date a lot easier.

[ccross2]

Closing as already covered by existing distribution: CI publishes a .deb on every build (the build-deb job / release assets), and the AUR carries visage, visage-git, and visage-bin (maintained by @SelfRef) for Arch users. A dedicated PPA adds recurring Launchpad account + GPG-signing + per-series source-build maintenance that isn't justified by the current install story. Happy to reopen if a maintainer wants to own that upkeep long-term.