Add More Usage Examples

Our current [examples](https://github.com/aafre/artisan-engine/tree/main/examples) are great, but more practical, real-world examples would make it even easier for new users to understand the power of Artisan Engine.

Create a new Python script in the examples/ directory that solves a common problem using the OpenAI-compatible endpoint.

**Some ideas:**

- 03_data_classification.py: Take a product review and classify it into categories like "Bug Report," "Feature Request," or "General Feedback."
- 04_code_generation.py: Take a natural language description (e.g., "a Python function that takes two numbers and returns their sum") and generate the corresponding code in a JSON object.
- 05_text_summarization.py: Take a long piece of text and extract a structured summary with a title, a one-sentence summary, and a list of key bullet points.

**Acceptance Criteria**
- A new, runnable script is added to the examples/ directory.
- The script should be well-commented and easy to understand.