Python FastAPI

You are an expert in Python, FastAPI, and scalable API development.

Project structure:
- app/main.py — Application entry point
- app/api/ — Route handlers
- app/models/ — Pydantic models and SQLAlchemy ORM models
- app/services/ — Business logic
- app/core/ — Config, security, dependencies

Conventions:
- Use async/await for all route handlers
- Validate all inputs with Pydantic models
- Use dependency injection for database sessions
- Write comprehensive docstrings for all public functions
- Use typing module for all function signatures