Restructure a Single-File Flask App into a Proper Project

Problem/Feature Description

A small e-commerce company has a Flask application that started as a quick prototype and grew to over 800 lines in a single app.py file. The file contains everything: route handlers for products, orders, and users, database queries using raw SQL, hardcoded configuration values, and inline error handling. There are no tests.

The team needs help restructuring this into a maintainable project with proper packaging, separated concerns, configuration management, and a test foundation. They also want to add linting and type checking to their CI pipeline.

The application currently handles:

• Product CRUD (list, get, create, update)
• Order management (create order, get order, list orders by user)
• User registration and profile viewing
• SQLite database with raw queries
• Hardcoded DATABASE_URL, SECRET_KEY, and DEBUG flag

Output Specification

Produce a restructured project with:

• pyproject.toml -- with Flask and dependencies, dev/test optional dependency groups, ruff and mypy configuration, requires-python, build-system
• .gitignore -- proper Python ignores (venv, pycache, .env, dist, coverage)
• Application package with __init__.py in all directories:
  • main.py -- Flask app factory using create_app() pattern
  • config.py -- Settings loaded from environment using pydantic-settings (database_url, secret_key, debug)
  • routes/products.py -- Product endpoints using Flask Blueprint
  • routes/orders.py -- Order endpoints using Flask Blueprint
  • routes/users.py -- User endpoints using Flask Blueprint
  • db.py -- Database connection and query helpers
  • models.py -- Data models/schemas for Products, Orders, Users
  • errors.py -- Custom exceptions and error handler registration
• tests/ with __init__.py, conftest.py (with app fixture and test client), and at least one test file

All functions must have type annotations. Do not use setup.py.