* Handle prerelease tags when publishing GitHub releases

- Derive `is_prerelease` and `make_latest` from the version format in preflight
- Mark suffixed versions (for example `1.2.3-alpha.1`) as prereleases
- Keep only plain `X.Y.Z` releases marked as latest
- Document prerelease/latest behavior in `docs/release.md`

* Force desktop auto-updates to stable latest channel

- set Electron updater channel to `latest`
- disable prerelease and downgrade updates regardless of app version