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/playbooks/site.yml

@@ -0,0 +1,25 @@
+---
+# Every stack, in dependency order. Each imported playbook also runs on its own
+# — see AGENTS.md, rule 2.
+#
+#   ansible-playbook playbooks/site.yml                    # converge everything
+#   ansible-playbook playbooks/site.yml --tags metrics     # one stack
+#   ansible-playbook playbooks/site.yml -e pull=always     # update everything
+#
+# Order matters. The reverse proxy owns proxy-net and the vhost configuration
+# that every other stack registers against, so it goes first; banner.yml writes
+# into the proxy's html directory, so it goes second.
+
+- name: Reverse proxy
+  ansible.builtin.import_playbook: reverse-proxy.yml
+- name: Default vhost banner
+  ansible.builtin.import_playbook: banner.yml
+- name: Metrics
+  ansible.builtin.import_playbook: metrics.yml
+
+- name: Static site
+  ansible.builtin.import_playbook: static-site.yml
+- name: Webapp
+  ansible.builtin.import_playbook: webapp.yml
+- name: Webapp staging
+  ansible.builtin.import_playbook: webapp-staging.yml