Improve UI Examples in examples/ui

Summary

This PR includes multiple improvements and refinements in examples/ui including new UI feature.

Key updates include:

1. Fix Issues:

• Fixed unable to run command_line.py with default argument
• Moved ChatAnthropic import inside the if statement to prevent unnecessary imports.

2. New UI Feature - Streamlit Demo:

• Added a Streamlit-based UI (streamlit_demo.py) for interacting with the tool.
• Included instructions for running the Streamlit demo.

3. Code Refactoring:

• Rearranged imports to follow PEP 8 guidelines.
• Refactored parts of the script into functions for better modularity and maintainability.
• Added boilerplate code to prevent accidental invocation of scripts.

4. Environment Variable Handling:

• Implemented a check to ensure api_key is loaded properly with dotenv.
• Reverted and re-applied changes related to API key handling for correctness.

5. Documentation Updates:

• Added a README for UI components, explaining different interfaces available.

✅ Tested with following

1. ✅ Run the command-line version:

   python command_line.py

2. ✅ Test the Gradio UI:

   python gradio_demo.py

3. ✅ Test the Streamlit UI:

   python -m streamlit run streamlit_demo.py

4. ✅ Verify that all environment variables (e.g., OPENAI_API_KEY) are loaded properly.

Impacts

1. 💡Low risk – The changes mainly involve UI refactoring, with no browser-use logic changes
2. ❤️Added Streamlit UI example, can reach a wider audience

Streamlit UI: