[Easy] Add credential event logging

[Josie123-Dev]

Task Description

Implement comprehensive event logging in contracts:

• Log all credential events
• Include event details
• Emit structured events
• Maintain event history
• Provide event query

Requirements

• Event logging
• Detail inclusion
• Structured events
• History maintenance
• Event query

Acceptance Criteria

• Events are logged
• Details are included
• Events are structured
• History is maintained
• Query works