Add structured log for KYC status changes including previous status, new status, and reviewer wallet

[Chucks1093]

Summary

KYC status changes (approve, reject, revoke) are security-sensitive events that require a complete audit trail. An info-level log on every status change would give operators a record of who changed which wallet's status and when.

Scope

• Emit an info-level log on every KYC status change with fields: wallet, previous_status, new_status, reviewer_wallet, changed_at
• Log emitted after the status is persisted, before the response is sent
• reviewer_wallet is the admin wallet that triggered the change
• Log emitted for approve, reject, and revoke actions

Acceptance Criteria

• Info log emitted on approve with all five fields
• Info log emitted on reject with all five fields
• Info log emitted on revoke with all five fields
• previous_status reflects the status before the change
• Log emitted after persistence (not before)

ETA: 12 hours

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