feat: working XFCE + RustDesk online on VPS tmux

- Add start-rd-desktop.sh: Xvfb :99 + xfwm4 + xfce4-panel + RustDesk client
- Add rustdesk-vps.service (Type=simple, but systemd kills processes) → use tmux instead
- Update README.md with VPS architecture (Xvfb + xfce4-session + RustDesk)
- Update VPS section: tmux persistent session instead of systemd
- RustDesk ID: 458564614, password: retrowest
- Ports 21115-21119 open in UFW for Docker server (optional)
- XFCE desktop confirmed working (xfdesktop + xfwm4 + panel)

Note: systemd ExecStartPre kills background processes (Xvfb, xfce4).
Solution: tmux detached session 'rd' with start-rd-desktop.sh

config/vps/start-rd-desktop.sh

@@ -0,0 +1,51 @@
+#!/bin/bash
+# RustDesk + XFCE Desktop Auto-Start for VPS
+# Systemd runs this script; script waits for Xvfb to exit
+
+set -e
+
+# Kill old
+pkill -9 -f rustdesk 2>/dev/null || true
+pkill -9 -f xfce4-session 2>/dev/null || true
+pkill -9 Xvfb 2>/dev/null || true
+rm -f /tmp/.X11-unix/X99 /tmp/.X*-lock
+sleep 2
+
+# Start Xvfb :99
+Xvfb :99 -screen 0 1920x1080x24 -ac +extension RANDR +extension RENDER +extension GLX > /dev/null 2>&1 &
+XVFB_PID=$!
+sleep 3
+
+# Wait for display ready
+export DISPLAY=:99
+export XAUTHORITY=/root/.Xauthority
+for i in $(seq 1 30); do
+    xrandr --listmonitors > /dev/null 2>&1 && break
+    if ! kill -0 $XVFB_PID 2>/dev/null; then
+        echo "ERROR: Xvfb died"
+        exit 1
+    fi
+    sleep 1
+done
+
+xrandr --listmonitors > /dev/null 2>&1 || { echo "ERROR: Display :99 not ready"; exit 1; }
+
+# Start XFCE desktop in background
+nohup dbus-run-session -- xfce4-session > /tmp/xfce-session.log 2>&1 &
+echo "XFCE PID: $!"
+sleep 5
+
+# Wait for window manager
+for i in $(seq 1 20); do
+    ps aux | grep xfwm4 | grep -v grep > /dev/null 2>&1 && break
+    sleep 1
+done
+
+# Start RustDesk client in background
+nohup dbus-run-session -- /usr/share/rustdesk/rustdesk --server > /tmp/rustdesk-session.log 2>&1 &
+echo "RustDesk PID: $!"
+sleep 3
+
+# Wait for Xvfb (main process) - systemd tracks this script
+# If Xvfb dies, systemd will restart the service
+wait $XVFB_PID