feat(runners): expose Runners management (list/register/delete)

[polaz]

👍 React to this issue if you need this feature — helps us prioritise.

Problem

GitLab Runners are the workhorses of CI. Admins/maintainers regularly need to list, register, and decommission runners. We expose nothing here.

Investigation done (current state)

Verified against src/entities/:

• ✅ TokenScopeDetector.ts recognises create_runner and manage_runner scopes (good — we can hint at availability)
• ✅ entities/shared.ts reads shared_runners_enabled, group_runners_enabled, runners_token, runner_token_expiration_interval on project schema — but we expose no actions
• ❌ No entity runners/ exists, no grep hit for runner CRUD

Re-verify before coding:

grep -rIni 'runner' src/entities/ | grep -v shared

Acceptance criteria

• New entity src/entities/runners/ with:
  • browse_runners actions: list_all (admin), list_owned (current user), list_project, list_group, get, list_jobs (jobs run by a runner)
  • manage_runner actions: create_authentication_token (new GitLab 16+ runner registration flow), update, pause/resume, delete, reset_authentication_token
• Permission: create_runner / manage_runner scopes; admin probe (feat(context): probe admin_mode elevation and expose in whoami #434) for instance-level list
• Integration test: register ephemeral runner, list, delete

GitLab API

• Endpoints: /api/v4/runners, /projects/:id/runners, /groups/:id/runners
• Tier: Free
• Important: GitLab 16+ uses new authentication-token-based registration; legacy registration-token flow is removed
• Docs: https://docs.gitlab.com/api/runners/

Estimate

1d

Context

Found during GitLab 18→19 API landscape analysis.