[NV29] Mainnet upgrade

# Summary

Prepare and drive network upgrade on mainnet with Forest

# Completion Criteria

- [ ] Correct actors bundle used Forest
- [ ] Schedule agreed with other implementations
- [ ] Checked that state root produces same result on a synthetic epoch
- [ ] Someone present during the upgrade to confirm all works fine and provide support if it doesn't
- [ ] Comms on relevant Slack channels and GH

# Additional Links & Resources

Start with the completion criteria in this issue, which cover the actors bundle, implementation coordination, synthetic-epoch state-root checks, upgrade support, and communications. No files, tests, or entry points are named, so completion depends on coordinating the mainnet upgrade and confirming each listed criterion.

Written by the indexing model from the issue text.