Creates .forgejo/workflows/ci.yml that runs the repo's single-source-of-truth
check gate (./script/checks) on every push to main and every pull request.
Triggers: push to main, pull_request
Concurrency: group by workflow+ref, cancel-in-progress true
Steps: actions/checkout@v4, actions/setup-node@v4 (node-version-file: .nvmrc),
corepack + pnpm i --frozen-lockfile, then ./script/checks.
Part of bead mailship-e77.
