Reserve fixed IPs on the lava network so Caddy can always start

lava was created by hand without an ip_range, so any container could be
given Caddy's fixed IP (172.20.0.5). After a reboot the containers race
for the low addresses and Caddy often fails with "Address already in use".

- The docker role now creates lava as 172.20.0.0/16 with dynamic
  addresses limited to 172.20.128.0/17, so 172.20.0.x is free for fixed
  IPs, and warns if the network still has the old layout.
- Gitea gets fixed IP 172.20.0.6 once the network has the reserved range,
  since its ufw-docker SSH rule points at its IP.
- ufw-docker allow rules for Caddy (80, 443) and Gitea SSH are managed by
  the playbook and follow IP changes.
- migrate-lava-network.yml recreates the existing network once: it takes
  down every compose project on lava (volumes kept), recreates the
  network, and brings them back up, Caddy first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

roles/docker/templates/gitea-compose.yml.j2

@@ -30,6 +30,11 @@ services:
     extra_hosts:
       - '{{ subdomains.auth }}:{{ docker.hairpin_ip }}'
       - '{{ subdomains.git }}:{{ docker.hairpin_ip }}'
+{% if lava_reserved | default(false) | bool %}
+    networks:
+      default:
+        ipv4_address: {{ docker.gitea_ip }}
+{% endif %}
   runner:
     image: gitea/act_runner:nightly
     restart: unless-stopped