Remove the aictrl github and aictrl pr commands #188

Decision

Remove upstream's GitHub Actions installer/runner aictrl github (src/cli/cmd/github.ts, ~1.6k lines) and aictrl pr (src/cli/cmd/pr.ts). Also remove their dependencies if nothing else uses them (@actions/*, @octokit/*), and the repo's /github action directory if it only exists for them. Callers run aictrl run in their own workflows instead. Invoking either command fails with a clear "removed" message.

Rules

• Delete the code, its tests and any dependencies only it uses. The net diff should be strongly negative. No default-off switch and no opt-in to bring it back.
• Compatibility shims only where existing configs or stored data would otherwise break:
  • config keys still load as deprecated no-ops, with one warning;
  • old sessions still load;
  • removed commands fail with a clear "was removed" error.
• Tracked under the headless optimisation epic Epic: Optimise headless run execution #153.