Add the compose_stack role, inventory and playbooks

One role that syncs a payload and brings the stack up, configured entirely
through stack_* variables, plus six playbooks that each demonstrate one part
of that contract. Every playbook runs standalone and is tagged with its
stack name, so site.yml --tags <stack> works.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

ansible/ansible.cfg

@@ -0,0 +1,20 @@
+# Ansible only discovers an ansible.cfg in the current working directory, so
+# every command in this repository is run from ansible/. See "Getting started"
+# in the README, and ANSIBLE_CONFIG for the CI case.
+[defaults]
+inventory = inventory/hosts.yml
+roles_path = roles
+retry_files_enabled = False
+stdout_callback = default
+callback_result_format = yaml
+display_skipped_hosts = False
+interpreter_python = auto_silent
+
+# CI runners are ephemeral, so a known_hosts file never survives to be checked
+# against. Turn this back on if you deploy from a durable control node or put a
+# bastion in front of the hosts — it is the one setting here worth revisiting.
+host_key_checking = False
+
+[ssh_connection]
+pipelining = True
+ssh_args = -o ControlMaster=auto -o ControlPersist=60s -o ServerAliveInterval=30