Improve database schema and add migration support

[kmuwanga83]

📌 Problem

Database structure may not be well documented or version-controlled.

🎯 Objective

Improve database design and maintainability.

✅ Tasks

• Review existing schema
• Normalize tables if necessary
• Add migration support (Flyway/Liquibase)
• Document database structure

🧪 Acceptance Criteria

• Database schema is documented
• Migrations can be run easily
• Schema supports scalability