Adds automated workflow that creates a PR from nightly → main every
Monday at 9:00 AM UTC for scheduled release promotion.
Features:
Pre-flight health check verifies critical workflows are passing
Skips PR creation if nightly has no new commits
Detects existing PRs and adds comments instead of duplicates
Labels PRs with 'automated' and 'weekly-promotion'
Creates GitHub issue on failure for visibility
Manual trigger via workflow_dispatch with reason input
NO auto-merge - requires human review and approval
This gives early-week visibility into nightly changes and prevents
Friday surprises from untested code reaching main.
b43a5dbae8