Implement input validation for patient registration and updates

[kmuwanga83]

📌 Problem

Patient data may be stored without proper validation, leading to inconsistent or invalid records.

🎯 Objective

Ensure all patient inputs are validated before saving.

✅ Tasks

• Add validation for:
  • name (not empty)
  • age (valid range)
  • email/phone format
• Use validation annotations (e.g., @NotNull, @Email)
• Return meaningful error messages

🧪 Acceptance Criteria

• Invalid inputs are rejected
• Clear error messages are returned
• Data integrity is improved