add Terraform + Ansible infrastructure for GCP deployment

Provisions e2-micro VM (us-east1-b, free tier) with static IP, SSH and
web firewall rules, Docker + Caddy startup script, and IAM bindings for
Firestore and GCS access via ADC. Imports existing drb-calls bucket and
c2-server Firestore database into state. Ansible roles handle first-time
setup (swap, docker group) and all subsequent deploys via rsync + docker
compose, with secrets managed via Ansible Vault. DNS stays on AWS Route 53.

infra/ansible/inventory.ini.example

@@ -0,0 +1,8 @@
+# Copy to inventory.ini and replace SERVER_IP with the Terraform output.
+# Get it with: cd ../terraform && terraform output server_ip
+
+[drb]
+SERVER_IP ansible_user=drb ansible_ssh_private_key_file=~/.ssh/id_ed25519
+
+[drb:vars]
+ansible_python_interpreter=/usr/bin/python3