Periodically pushes a genuinely empty commit (no file changes) to your GitHub repo, roughly every 15–30 minutes. No "activity update" banners — just clean, empty commits with generic messages like chore: housekeeping.

• Runs on a 15-minute cron (the fastest a Free Val Town account allows).
• Each run decides whether to commit based on a random roll and how long it's been since the last commit, so the actual gaps vary — usually 15–30 min, sometimes more, never past ~45 min.
• Empties are made through the GitHub Git Data API: it reuses the current commit's tree, creating a new commit with zero file changes.

Set these environment variables on the val: