feat(ansible): idempotent role-based host config for both production VMs

common/firewall/docker-tls/platform/lab-host/monitoring-agent/backup roles,
orchestrated by site.yml with the ordering that matters (firewall/TLS land
before the services that depend on them). Ansible Vault for secrets, no new
tool introduced for this project's modest secret surface. Explicit
dev/staging/production environment separation, no secrets committed
(.gitignore covers vault plaintext, TLS keys, Terraform state, *.env).

Validated: ansible-playbook --syntax-check clean.

infra/ansible/roles/docker-tls/defaults/main.yml

@@ -0,0 +1,6 @@
+---
+# Local path (on the machine running ansible-playbook, NOT on either VM) holding the cert
+# bundle generated by infra/scripts/docker-tls/generate-docker-tls.sh. The CA private key
+# (ca-key.pem) is deliberately never copied to either host by this role — only its public
+# ca.pem, plus the one cert/key pair each host actually needs.
+docker_tls_local_bundle_dir: "{{ lookup('env', 'ROOTNODE_TLS_BUNDLE_DIR') | default('/does/not/exist', true) }}"