A version bump that got left behind — fixing it with a single source of truth and a `--check` gate

Bumping a desktop app's version number sounds like a one-line change. In practice it can mean editing five different files at once. During one release, exactly one of those files got missed, and an installer nearly got built carrying the old version number.

Note: A "version bump" just means incrementing the version number — say, from 1.6.9 to 1.6.10. The operation sounds trivial, but it can end up scattered across multiple files in practice.

What happened

This app's version number lives in five separate places:

The VERSION variable in version.py