🧪 Add unit tests for models

Description

No test directory exists. Need to add comprehensive unit tests for all models.

Models to test

• User model (authentication, validations, associations)
• Recipe model (validations, Active Storage, Action Text)
• Category model (validations, associations)
• Basket model (associations, uniqueness)

Setup needed

• Create test/ directory structure
• Configure test database
• Add fixtures or factories (consider FactoryBot)
• Set up test helpers

Testing framework

Using Rails built-in Minitest or consider RSpec