Add custom CI runner images: self-hosted registry, ssh-alpine image, biweekly rebuild

- Enabled GitLab Container Registry on its own subdomain via NPM/mkcert
- Built minimal ssh-alpine image (Alpine + OpenSSH, key-only auth)
- Docker-outside-of-Docker build pipeline reusing the host socket, no DinD
- Forced --pull --no-cache builds so scheduled rebuilds pick up real upstream updates
- Biweekly Pipeline Schedule (cron: 0 3 */14 * *)
- Registry cleanup policy to prevent unbounded tag growth
- Documented the Tailscale/Pi-hole DNS conflict and other gotchas hit along the way

docs/Home.md

@@ -17,6 +17,7 @@ Documentation for a self-hosted homelab running entirely on Docker Compose. This
 - [DockScope](DockScope.md)
 - [Ansible Playbooks](AnsiblePlaybooks.md)
 - [GitLab CI/CD](GitLab-CICD.md)
+- [Custom CI Runner Images](CI-Custom-Images.md)
 - [Elastic Stack (ELK) — Lab](ElasticStack.md)
 
 ## At a glance