feat: add VNC toggle to dashboard

- Add x11vnc + noVNC container with Traefik reverse proxy
- Add /api/vnc_status and toggle_vnc action to FastAPI
- Add VNC toggle button to BotVPS dashboard
- VNC off by default, controlled via dashboard

vnc/docker-entrypoint.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+set -e
+
+# Ensure X11 socket exists and has correct permissions
+chmod 1777 /tmp/.X11-unix 2>/dev/null || true
+chmod 666 /tmp/.X11-unix/X10 2>/dev/null || true
+
+# Start x11vnc — connects to host XFCE on display :10
+x11vnc \
+    -display :10 \
+    -nopw \
+    -bg \
+    -listen 0.0.0.0 \
+    -xkb \
+    -ncache 10 \
+    -ncache_cr \
+    -forever \
+    -shared \
+    -noshm \
+    -rfbport 5900
+
+# Start websockify → WebSocket proxy for noVNC
+exec websockify \
+    --web /usr/share/novnc \
+    0.0.0.0:6080 \
+    localhost:5900