Recipe Collection App

Problem/Feature Description

Build a backend for a personal recipe collection app using Python and Flask. Use SQLite as the database (this is a single-user app running locally).

The system needs:

• Recipes: title, description, prep time in minutes, cook time in minutes, servings, difficulty level (easy/medium/hard), created and updated timestamps.
• Ingredients: each recipe has multiple ingredients with name, quantity, and unit (e.g. "2 cups flour"). Ingredients belong to exactly one recipe. Deleting a recipe should delete its ingredients.
• Tags: recipes can have multiple tags (e.g. "vegetarian", "quick", "dessert"). Tags are shared across recipes (many-to-many relationship).
• CRUD for recipes including their ingredients (create recipe with ingredients in one operation, update recipe and replace its ingredients atomically).
• Search recipes by tag, by ingredient name (partial match), or by title (partial match).
• List recipes sorted by most recently updated.

Output Specification

Produce:

• app/database.py -- Database connection and schema setup
• app/models.py -- Data classes or Pydantic models
• app/routes.py -- Flask route handlers
• app/app.py -- Flask application factory
• requirements.txt -- With dependencies

Complete Python code, no placeholders or TODO comments.