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/caddy/handlers/main.yaml

@@ -0,0 +1,6 @@
+---
+- name: Reload Caddy
+  # Caddy validates before it applies, so a mistake here leaves the running
+  # config untouched and fails the play loudly.
+  command: "docker exec -w /etc/caddy {{ caddy_container }} caddy reload"
+  listen: Reload Caddy