Shelf Drive v4.0.1

Interface

• Added a recurring background update check every six hours so a running app notices new releases without a restart, alongside the existing startup check.

Distribution

• Made 4.0.1 the first published desktop release; the in-app updater now serves signed manifests from this repository's releases, so installs update in place instead of downloading from GitHub manually.

CI packaging fixtures

Immutable packaging fixtures for the arch-package.yml contract tests. Regenerate with the Arch fixture build workflow, then pin the new SHA256, filename, and version in arch-package.yml.