Add database seed data for development and testing

[kmuwanga83]

📌 Problem

The system starts with an empty database, making testing difficult.

🎯 Objective

Provide sample data for easier development and demonstration.

✅ Tasks

• Add seed data for:
  • patients
  • doctors
  • appointments
• Provide SQL scripts or initializer class
• Document how to load seed data

🧪 Acceptance Criteria

• Sample data loads automatically or via script
• Developers can test features immediately
• Documentation explains usage