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/Dockerfile

@@ -0,0 +1,23 @@
+FROM debian:bookworm-slim
+
+RUN apt-get update && apt-get install -y \
+    x11vnc xvfb \
+    novnc websockify \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN mkdir -p /VNC && cd /VNC \
+    && ln -sf /usr/share/novnc/vnc.html vnc.html \
+    && ln -sf /usr/share/novnc/vnc_lite.html vnc_lite.html
+
+# X11 socket from host (display :10)
+# Host / is mounted at /host_root by BotVPS compose
+VOLUME ["/tmp/.X11-unix:/host_x11/X11-unix:rw"]
+
+ENV DISPLAY=:10
+
+COPY docker-entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+
+EXPOSE 6080
+
+ENTRYPOINT ["/entrypoint.sh"]