Switch auto-updates to GitHub Releases and drop S3

[JZimz]

We're already publishing releases to both S3 and GitHub, which is redundant. The auto-updater currently points to S3 (romie.jzimz.com), but GitHub Releases can handle this natively with electron-updater.

Switching to GitHub-only would:

• Eliminate AWS costs
• Simplify deployment (one destination instead of two)
• Make beta channels easier to implement later

This means updating the auto-updater config to use UpdateSourceType.ElectronPublicUpdateService, removing the S3 publisher from forge config, and simplifying the release workflow to just use make instead of conditionally using publish.