Add minimal agent example demonstrating sandboxed file I/O

examples/minimal-agent/Dockerfile

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+FROM python:3.11-slim
+
+WORKDIR /app
+COPY example_agent.py /app
+
+RUN useradd -m agent && chown -R agent:agent /app
+USER agent
+
+CMD ["python", "example_agent.py"]
+

examples/minimal-agent/README.md

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+# Minimal Example Agent
+
+A tiny example showing how to run an agent inside a container:
+- Creates `input.txt` if missing
+- Reads it, uppercases content
+- Writes the result to `output.txt`
+
+## Run
+
+### Linux/macOS
+```bash
+docker build -t cua-agent-example examples/minimal-agent
+docker run --rm -v $(pwd)/examples/minimal-agent:/app cua-agent-example

examples/minimal-agent/example_agent.py

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+import os
+
+INPUT_FILE = "input.txt"
+OUTPUT_FILE = "output.txt"
+
+def run_agent():
+    if not os.path.exists(INPUT_FILE):
+        with open(INPUT_FILE, "w") as f:
+            f.write("Hello from Cua!\n")
+
+    with open(INPUT_FILE, "r") as f:
+        data = f.read()
+
+    processed = data.upper()
+
+    with open(OUTPUT_FILE, "w") as f:
+        f.write(processed)
+
+    print(f"Processed file written to {OUTPUT_FILE}")
+
+if __name__ == "__main__":
+    run_agent()

examples/minimal-agent/input.txt

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+Hello from Cua!

examples/minimal-agent/output.txt

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+HELLO FROM CUA!