Tag completed milestones with git tags

[the-gigi]

Summary

When a milestone is completed, create a git tag (e.g. milestone-<number>) so we can always check out the state of the repo at that point.

Details

• On milestone completion, create a git tag like milestone-<number>
• Tag should be pushed to the remote
• Applies to both genesis and ronny-learns-ai repos

Acceptance criteria

• Completing a milestone creates a git tag
• Tag is pushed to the remote