Add headless Agentbox environment spike

Co-authored-by: codegirl007 <codegirl-007@users.noreply.github.com>

agentbox/environment/Dockerfile

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+FROM debian:bookworm-slim AS builder
+
+RUN apt-get update \
+    && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+        build-essential \
+        libx11-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY examples/mover/main.c /src/main.c
+RUN cc -std=c11 -O2 -Wall -Wextra -Werror /src/main.c -lX11 -o /mover
+
+FROM debian:bookworm-slim
+
+RUN apt-get update \
+    && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+        libx11-6 \
+        openbox \
+        scrot \
+        x11-utils \
+        xdotool \
+        xvfb \
+    && rm -rf /var/lib/apt/lists/* \
+    && useradd --create-home --uid 10001 agentbox
+
+COPY --from=builder /mover /opt/agentbox/mover
+COPY environment/entrypoint.sh /opt/agentbox/entrypoint.sh
+RUN chmod 0755 /opt/agentbox/entrypoint.sh /opt/agentbox/mover
+
+USER agentbox
+ENV DISPLAY=:99
+ENTRYPOINT ["/opt/agentbox/entrypoint.sh"]

agentbox/environment/entrypoint.sh

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+#!/bin/sh
+set -eu
+
+export HOME=/tmp/home
+export XDG_RUNTIME_DIR=/tmp/runtime
+mkdir -p "$HOME" "$XDG_RUNTIME_DIR"
+chmod 0700 "$XDG_RUNTIME_DIR"
+
+cleanup() {
+    rm -f /tmp/agentbox-ready
+    kill "${OPENBOX_PID:-}" "${XVFB_PID:-}" 2>/dev/null || true
+    wait "${OPENBOX_PID:-}" "${XVFB_PID:-}" 2>/dev/null || true
+}
+
+terminate() {
+    trap - EXIT INT TERM
+    cleanup
+    exit 0
+}
+
+trap cleanup EXIT
+trap terminate INT TERM
+
+Xvfb "$DISPLAY" -screen 0 640x480x24 -nolisten tcp -noreset &
+XVFB_PID=$!
+
+attempt=0
+until xdpyinfo -display "$DISPLAY" >/dev/null 2>&1; do
+    attempt=$((attempt + 1))
+    if [ "$attempt" -ge 100 ]; then
+        echo "Xvfb did not become ready" >&2
+        exit 1
+    fi
+    sleep 0.05
+done
+
+openbox --sm-disable >/tmp/openbox.log 2>&1 &
+OPENBOX_PID=$!
+touch /tmp/agentbox-ready
+
+while :; do
+    sleep 3600 &
+    wait $!
+done