Use real desktop stack in tests

docker/test-agent/Dockerfile

@@ -17,12 +17,25 @@ RUN --mount=type=cache,target=/usr/local/cargo/registry \
 
 FROM node:22-bookworm-slim
 RUN apt-get update -qq && \
-    apt-get install -y -qq --no-install-recommends ca-certificates bash libstdc++6 > /dev/null 2>&1 && \
+    apt-get install -y -qq --no-install-recommends \
+      ca-certificates \
+      bash \
+      libstdc++6 \
+      xvfb \
+      openbox \
+      xdotool \
+      imagemagick \
+      x11-xserver-utils \
+      dbus-x11 \
+      xauth \
+      fonts-dejavu-core \
+      xterm \
+      > /dev/null 2>&1 && \
     rm -rf /var/lib/apt/lists/*
 
 COPY --from=builder /sandbox-agent /usr/local/bin/sandbox-agent
 
 EXPOSE 3000
 
-ENTRYPOINT ["sandbox-agent"]
+ENTRYPOINT ["/usr/local/bin/sandbox-agent"]
 CMD ["server", "--host", "0.0.0.0", "--port", "3000", "--no-token"]