[1.1 User Management] Create user model with hashed passwords #1

Milestone: Milestone 1: Backend API (Python)
Category: 1.1 User Management
Task: Create user model with hashed passwords

Task Description

Implement a secure user model that supports password hashing, basic user profile fields, and registration logic.

Requirements

• Use strong password hashing
• Add registration endpoint that hashes passwords before saving
• Validate uniqueness of email and/or username
• Implement basic error handling and validation

Testing Requirements

• Unit test password hashing
• Test user creation and duplicate prevention
• Confirm no plain-text passwords stored in DB