Add basic schema

[bostdiek]

Description:
Define the initial backend data models and schemas for recipes, ingredients, and users using Pydantic (or equivalent ORM base).

Developer Story:
As a developer, I want to define clean schema models so I can build robust APIs and validate data consistently.

Acceptance Criteria:
• A models/ or schemas/ directory is created with:
• Recipe
• Ingredient
• User (or placeholder for now)
• Each model has appropriate fields (e.g., title, ingredients list, instructions).
• Models are defined using Pydantic or SQLAlchemy (or both).
• Types and validations are added (e.g., required fields, string lengths).
• At least one unit test checks model validation.