feat(deploy): Ansible provisioning for prod hosts (Stage 18)

Idempotent playbooks under deploy/ansible/ prepare both production hosts:
docker-ce + compose plugin, a non-sudo deploy service account holding the CI
deploy key, key-only sshd, default-deny ufw, fail2ban, unattended upgrades and
chrony. The main host also opens 80/443/9443 and creates the external edge
network; the tg host verifies direct Bot API egress (the no-VPN assumption).

The application is deployed separately by the prod-deploy workflow (later
phase), running as the deploy account this playbook provisions.

deploy/ansible/site.yml

@@ -0,0 +1,31 @@
+---
+# Stage 18 host provisioning. Idempotent: safe to re-run after a host resize.
+# Prepares hosts only (docker, hardening, service account, firewall); the
+# application is deployed separately by .gitea/workflows/prod-deploy.yaml.
+
+- name: Common baseline (both hosts)
+  hosts: prod
+  become: true
+  pre_tasks:
+    - name: Require a well-formed CI deploy public key
+      ansible.builtin.assert:
+        that:
+          - deploy_ci_pubkey | length > 0
+          - deploy_ci_pubkey is search('^(ssh|ecdsa)-')
+        fail_msg: >-
+          deploy_ci_pubkey is empty or malformed. Generate the key first
+          (see deploy/ansible/README.md) or override deploy_ci_pubkey_path.
+  roles:
+    - common
+
+- name: Main stack host
+  hosts: main
+  become: true
+  roles:
+    - main
+
+- name: Telegram bot host
+  hosts: tg
+  become: true
+  roles:
+    - tg