Add Advanced Python Tutor Bot Gradio app, prompt templates, and docs

[arshad831]

Motivation

• Provide a beginner-friendly interactive tutor that explains Python concepts, debugs code, runs quizzes, and suggests improvements using an LLM-backed chat UI.
• Ship a minimal runnable project layout with guidance for local API key configuration and dependency management.

Description

• Add app.py which builds a Gradio chat interface (build_app) and implements request handling via get_tutor_response, message construction (build_messages), and history conversion (_history_to_messages).
• Add prompts.py containing reusable PROMPT_TEMPLATES and MODE_DESCRIPTIONS for the four tutor modes: Explain Concept, Debug Code, Quiz Me, and Improve Code.
• Add project metadata and usage instructions in README.md, include runtime dependencies in requirements.txt, and provide an .env.example plus .gitignore to manage OPENAI_API_KEY and local files.
• Use python-dotenv to load a local .env, validate the OPENAI_API_KEY, set a SYSTEM_PROMPT, and call the OpenAI client with model gpt-4.1-mini and temperature 0.4.

Testing

• No automated tests were added or executed for this change.

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Codex Task