🔧 Fix Headplane UI configuration and enable external access

- Update docker-compose.yml: simplify environment variables
- Fix headplane-config/config.yaml with proper configuration:
  * Add required server section with correct cookie_secret (32 chars)
  * Configure headscale connection with API key
  * Enable external access via 192.168.0.151:3000/admin/
- Resolve configuration validation errors
- Headplane UI now fully accessible and functional

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

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

docker-compose.yml

@@ -30,15 +30,8 @@ services:
     restart: unless-stopped
     environment:
       - TZ=Asia/Seoul
-      - HOST=0.0.0.0
-      - PORT=3000
       - HEADSCALE_URL=http://headscale:8080
-      - ROOT_API_KEY=${HEADSCALE_API_KEY}
-      - HEADSCALE_INTEGRATION=docker
-      - HEADSCALE_CONTAINER=headscale
-      - COOKIE_SECRET=headscale-ui-secret-key-change-me
-      - COOKIE_SECURE=false
-      - DISABLE_API_KEY_LOGIN=false
+      - HEADSCALE_API_KEY=${HEADSCALE_API_KEY}
     volumes:
       - ./headplane-config:/etc/headplane
     ports: