feat: update configs for host+VPS with Intel VirtualHeads and dummy driver

- Host: 20-intel-virtual.conf with Driver intel + VirtualHeads 1
- VPS: xorg-dummy.service + rustdesk-dummy.service for CPU-only
- Updated README with dual setup (host Intel iGPU + VPS dummy)
- Verified: VIRTUAL1 primary after reboot, HDMI1 clone
- Verified: DUMMY0 primary on VPS without GPU

config/vps/rustdesk-dummy.service

@@ -0,0 +1,18 @@
+[Unit]
+Description=RustDesk Server with Dummy Display
+After=xorg-dummy.service
+Requires=xorg-dummy.service
+
+[Service]
+Type=simple
+User=root
+Environment="DISPLAY=:0"
+ExecStartPre=/bin/sleep 5
+ExecStart=/usr/lib/rustdesk/rustdesk --server
+Restart=always
+RestartSec=10
+StandardOutput=append:/var/log/rdtop-rustdesk.log
+StandardError=append:/var/log/rdtop-rustdesk.log
+
+[Install]
+WantedBy=multi-user.target