Automatically accept the session after g3 completes successfully,
but only if there are commits on the branch.
Changes:
- Add --accept flag to Run command (stripped, not passed to g3)
- Add has_commits_on_branch() helper using git rev-list --count
- Auto-accept triggers merge to main and cleanup when:
1. g3 exits successfully (exit code 0)
2. Branch has commits ahead of main
- Show warning if --accept set but no commits exist
Usage: studio run --agent carmack --accept
04e3c69b0a