Register Linux runner on forgejo (ubuntu-latest)

[ulises-c]

The Forgejo instance at ollie-server.tail01d63b.ts.net needs a runner for CI.

What: Install forgejo-runner on the Linux server hosting Forgejo.

Steps:

• Download forgejo-runner binary from code.forgejo.org
• forgejo-runner generate-config > /etc/forgejo-runner/config.yml
• Register with token from Forgejo → Settings → Actions → Runners
• forgejo-runner register --instance https://ollie-server.tail01d63b.ts.net --token <TOKEN> --name linux-runner --labels ubuntu-latest
• Set up systemd service for persistence

Prerequisites: curl, unzip, python3-pip, git

Why: Without this, lint/format/spellcheck CI jobs are stuck queued.