add: UniFi Controller LXC on pm4

Deployed for managing U7 AP in server closet testing.
IP: 10.4.2.242 (DHCP for now)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docs/CHANGELOG.md

@@ -2,6 +2,15 @@
 
 > **Purpose**: Historical record of all significant infrastructure changes
 
+## 2025-12-19
+
+### Network Upgrade Progress
+- **UniFi Controller**: Deployed LXC on pm4 for AP management
+  - IP: 10.4.2.242 (DHCP, will be assigned static via OPNsense later)
+  - Port: 8443 (HTTPS web UI)
+  - Deployed via ProxmoxVE community helper script
+  - Purpose: Manage U7 AP installed in server closet for testing
+
 ## 2025-12-18
 
 ### Service Additions