Add the menu-admin playbook

Deploys the menu app for one Site: pulls the tag, creates the data root, runs
the container against a config baked into the image, waits for health, verifies
the data directory, and points Caddy at the app with a marker it can update in
place. The parallel run uses a temporary hostname; cutover sets the retire
flags.

menu-admin/roles/network/tasks/main.yaml

@@ -0,0 +1,8 @@
+---
+- name: "Ensure {{ docker_network }} exists and Caddy is on it"
+  docker_network:
+    name: "{{ docker_network }}"
+    state: present
+    connected:
+      - "{{ caddy_container }}"
+    appends: yes