For CI, we just keep using GitHub Actions until we come up with something better lol. Actual pipelines are executed in flathub-infra/vorarbeiter either way, it could just stay there. We would need to extend vorarbeiter to accept webhooks from other forges and submit commit status elsewhere but that's largely it. We could eventually ask Buildkite nicely and replatform again.
flatpak-external-data-checker would need to learn how to open pull requests elsewhere. Similar thing applies to other scripts we're using here and there.
The rest is annoying legwork of figuring out how do we shift >3k repositories and collaborators elsewhere without losing maintainers. Maybe we just don't? New apps go to the new place, old apps get mirrored to the new place, maintainers can opt in to migration.
