Add structured log for each successful KYC document upload including file size and document type

[Chucks1093]

Summary

KYC document uploads are security-sensitive operations with no current log trail. An info-level log on each successful upload would give operators an audit record of what was submitted and when, without storing the file content.

Scope

• Emit an info-level log after each successful KYC document upload with fields: wallet, document_type, file_size_bytes, ipfs_cid, uploaded_at
• Log emitted after the IPFS upload succeeds and the CID is persisted
• File name and file content must not appear in the log
• document_type is the seller-selected type (e.g. 'passport', 'national_id')

Acceptance Criteria

• Info log emitted after successful upload with all five fields
• File name and content absent from log
• Log emitted after CID is persisted (not before)
• document_type matches the seller-selected value

ETA: 12 hours

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