Ownership Transfer Recording Endpoint

[mftee]

Description:

Implement a POST /transfer endpoint that anchors an ownership transfer event for a land document on the Stellar blockchain. This creates an auditable, on-chain record of a change in land ownership.

Requirements:

• Add a TransferRequest struct:

  pub struct TransferRequest {
      pub document_hash: String,
      pub from_owner: String,
      pub to_owner: String,
      pub transfer_date: String, // ISO 8601 date string
      pub transfer_reference: String, // legal reference number
  }

• Compute a transfer event hash: SHA-256(document_hash + from_owner + to_owner + transfer_date)
• Anchor this transfer hash to Stellar with memo prefix TRANSFER:<transfer_hash> (truncated)
• Store the full transfer record in a new Redis key transfer:<document_hash> as a JSON array (append each transfer to the array)
• Add a GET /transfer/:document_hash endpoint to retrieve the transfer history from Redis

Acceptance Criteria:

• Transfer hash is deterministic for the same inputs
• Multiple transfers for the same document are all stored and retrievable
• Unit tests for the transfer hash computation
• Returns 400 if transfer_date is not a valid ISO 8601 date