chore: Configure self-hosted GitHub Actions runner

[robertky]

Context

GitHub Actions workflow runs remain queued because the NTNU GitHub Enterprise installation has no shared runners. The course documentation requires a self-hosted runner on the group VM.

Tasks

• Confirm the group VM is reachable through the NTNU network or VPN
• Request repository admin access from it2810@idi.ntnu.no if needed
• Install and register a self-hosted GitHub Actions runner on the group VM
• Verify the runner has the self-hosted label and Node.js 24 available
• Confirm the CI workflow in PR chore: scaffold project template with tooling and CI #3 completes successfully

Blocks completion of #2.

[erikhfj]

Prep work is on PR #3 (commit 5a22a36):

• ci.yml now targets runs-on: [self-hosted, linux, x64] (matches a default-registered VM runner)
• Setup guide added: docs/ci-runner.md — install, register with --url https://git.ntnu.no/IT2810-H26/T19-Project-1, run as a service (svc.sh install && sudo ./svc.sh start), verification steps
• Stale ubuntu-latest runs cancelled (they could never start)

Next steps per the guide: (1) confirm repo admin access (email it2810@idi.ntnu.no if Settings → Actions is missing), (2) register the runner on the VM, (3) re-run the CI job. Note there is already a chore/6-self-hosted-runner branch — the guide and label change are covered by PR #3, so that branch can be rebased or closed to avoid duplicate work.

[erikhfj]

Confirmed: our team has push only (no admin/maintain) on this repo — the only admins are staff accounts. So runner registration is blocked on staff action.

Email to it2810@idi.ntnu.no is drafted requesting either repo admin for one member (to register the runner per docs/ci-runner.md) or that staff register a runner for us. Once access is granted, the rest of this issue is mechanical (guide is ready in PR #3).