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/roles/compose_stack/tasks/up.yml

@@ -0,0 +1,14 @@
+---
+- name: Bring the stack up
+  community.docker.docker_compose_v2:
+    project_src: "{{ stack_dest }}"
+    files: "{{ stack_files }}"
+    state: "{{ stack_state }}"
+    pull: "{{ stack_pull }}"
+    build: "{{ stack_build }}"
+    remove_orphans: true
+  # A compose file that interpolates ${PWD} — a common way to hand a host path to
+  # a sibling container — resolves it against the *invoking shell*, not the
+  # project directory. The module sets the process working directory but not PWD,
+  # so ${PWD} would silently become the SSH login directory. Set it explicitly.
+  environment: "{{ {'PWD': stack_dest} | combine(stack_env) }}"