Upgrade insurance price project to FastAPI ML Prediction API

[amanda622]

This PR upgrades the Insurance Price project from a basic ML demo into a production-style FastAPI prediction API with a simple web UI.
Changes include:

• Clean project structure with src/package layout
• Reproducible scikit-learn pipeline
• FastAPI endpoints for prediction and health check
• Simple web UI and Swagger documentation
• SQLAlchemy prediction logging
• Pytest test suite
• Ruff linting
• Docker support
• Updated README and deployment guide

Validation:

• 14 pytest tests passed
• Ruff check passed
• Docker image builds successfully
• Manual API test through Swagger returned prediction results

[amanda622]

Reviewed the changed files. Local validation passed: pytest, ruff, Docker build, and manual Swagger API test.