GRM-14: feat: add systemd template units and multi-instance Ansible support

- Add instance-scoped base data/config directories in defaults
- Create gitea-runner@.service.j2 template supporting Docker and binary modes
- Refactor service.yml to install systemd template unit instances
- Remove direct container lifecycle from docker_mode.yml (delegate to systemd)
- Add deregister.yml for runner deregistration on disable/remove
- Create lifecycle playbooks: start, stop, enable, disable, status, remove
- Update handlers, integration_test, docker_update, binary_update for template units

ansible/roles/gitea-runner/tasks/docker_update.yml

@@ -4,20 +4,9 @@
   changed_when: "'Downloaded newer image' in pull_result.stdout or 'Status: Downloaded' in pull_result.stdout"
   register: pull_result
 
-- name: Stop and remove existing gitea_runner container
-  ansible.builtin.command: docker rm -f gitea-runner-{{ runner_name }}
-  changed_when: remove.rc == 0
-  failed_when: remove.rc != 0 and 'No such container' not in remove.stderr
-  register: remove
-
-- name: Run updated gitea_runner daemon container
-  ansible.builtin.command: >
-    docker run -d
-    --name gitea-runner-{{ runner_name }}
-    --restart unless-stopped
-    -v /var/run/docker.sock:/var/run/docker.sock
-    -v {{ gitea_runner_data_dir }}:/data
-    {{ gitea_runner_docker_image }}:{{ gitea_runner_version | regex_replace('^v', '') }} daemon
-    --config /data/config.yaml
-  register: docker_run
-  changed_when: docker_run.rc == 0
+- name: Restart gitea-runner systemd instance
+  ansible.builtin.systemd:
+    name: "gitea-runner@{{ runner_name }}"
+    state: restarted
+    daemon_reload: true
+  when: systemd_available.stat.exists