Add Pi-hole host_vars for firewall ports

Allow required ports for Pi-hole:
- 22/tcp (SSH)
- 53/tcp, 53/udp (DNS)
- 80/tcp (Web admin)
- 443/tcp (HTTPS)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

host_vars/pihole.yml

@@ -0,0 +1,9 @@
+---
+# Pi-hole specific variables
+
+common_firewall_allowed_ports:
+  - "22/tcp"    # SSH
+  - "53/tcp"    # DNS
+  - "53/udp"    # DNS
+  - "80/tcp"    # Web admin
+  - "443/tcp"   # HTTPS (optional)