Add authentication components and logic

**As a** user  
**I need** to register and log in  
**So that** I can access personalized features

### Details and Assumptions
* Users should be able to sign up and log in securely.
* JWT tokens will be used for authentication.

### Acceptance Criteria
Given a user registers or logs in,  
When credentials are valid,  
Then the user gains access to restricted features.
