feat: scoped runner cleanup with ownership leases and disk admission

Extend stopped-container protection to an explicit lease contract
(org.oblachno.lease-until / org.oblachno.owner) honored by every cleanup
path. Consolidate the duplicated inline prune logic from docker-prune
and the healthcheck into a single tiered runner-cleanup.sh; remove the
unfiltered `system prune -af --volumes` / `volume prune` paths that could
wipe a job's volumes mid-run, and keep warm base images under pressure.

At critical disk usage the healthcheck now stops admitting new work
(stops gitea-runner.service once no CI job is in flight) and resumes it
automatically after recovery. The runner config declares capacity, and
the role refuses to install on production-marked hosts.

ansible/roles/gitea_runner/tasks/main.yml

@@ -1,4 +1,23 @@
 ---
+# Implements: REQ-6 (GRM-173) — a CI runner must never be installed on a
+# production host (production workloads must not share hardware with
+# arbitrary CI jobs, and runner cleanup logic assumes a dedicated host).
+- name: Check for production-host marker
+  ansible.builtin.stat:
+    path: "{{ gitea_runner_production_marker_path }}"
+  register: gitea_runner_production_marker
+
+- name: Fail on production hosts
+  ansible.builtin.fail:
+    msg: >-
+      Refusing to install a CI runner on a production host
+      (marker: {{ gitea_runner_production_marker_path }} present or
+      gitea_runner_on_production_host=true). Set
+      gitea_runner_allow_production_host=true to override.
+  when:
+    - not gitea_runner_allow_production_host
+    - gitea_runner_on_production_host or gitea_runner_production_marker.stat.exists
+
 - name: Include systemd availability check
   ansible.builtin.include_tasks: systemd_check.yml
 

ansible/roles/gitea_runner/tasks/prune.yml

@@ -1,4 +1,14 @@
 ---
+# Implements: REQ-2 (GRM-173) — shared scoped cleanup script used by both
+# the prune timer and the healthcheck disk-pressure tiers.
+- name: Create runner cleanup script
+  ansible.builtin.template:
+    src: runner-cleanup.sh.j2
+    dest: "{{ gitea_runner_cleanup_script_path }}"
+    owner: "{{ gitea_runner_service_user }}"
+    group: "{{ gitea_runner_service_user }}"
+    mode: "0755"
+
 - name: Create docker-prune user service file
   ansible.builtin.template:
     src: docker-prune.service.j2