[Easy] Implement credential hash verification

[Josie123-Dev]

Task Description

Add credential hash verification to contracts:

• Calculate credential hash
• Verify hash integrity
• Compare with stored hash
• Return verification result
• Emit verification events

Requirements

• Hash calculation
• Integrity check
• Hash comparison
• Result return
• Event emission

Acceptance Criteria

• Hash is calculated
• Integrity is verified
• Comparison works
• Result is returned
• Events are emitted