feat: add search by payref

[martinserts]

Description

Adds an API to search payments by payref

Closes #5

How Has This Been Tested?

Run the payment processor

$ cargo run                                                                                             
Starting Minotari Payment Processor...                                                                    
Database initialized.                                                                                     
Unsigned Transaction Creator worker started. Polling every 15 seconds.                       
Minotari Payment Processor started. Press Ctrl+C to shut down.
Transaction Signer worker started. Polling every 10 seconds.                            
Confirmation Checker worker started. Polling every 60 seconds. Required Confirmations: 5
Batch Creator worker started. Cycle interval: 120s.                                                       
Transaction Broadcaster worker started. Polling every 15 seconds.    
Axum API server listening on 0.0.0.0:9145

Fails on non-existent payref

curl -X 'GET' \
  'http://localhost:9145/v1/payments/ref/123' \
  -H 'accept: application/json'

{
  "error": "Payment not found"
}

Finds existing one

curl -X 'GET' \
  'http://localhost:9145/v1/payments/ref/d330d2c5f7c2242f87634ba7b2db408e24fa9dd9590354b421ba024f0467992a' \
  -H 'accept: application/json

{
  "payment_id": "b30b246c-735a-488f-81c9-5c2f6e814c17",
  "status": "CONFIRMED",
  "client_id": "pay_2_2",
  "account_name": "default",
  "recipient_address": "f2LUUip8F3LCQ6PyJvQiySCEpQyzTQSfvQF4YX3N9pY4rz4gAUprFgaL9JANYinYN2HGtKexmfX2odeNHfatoNhozaL",
  "amount": 2000000,
  "payref": "d330d2c5f7c2242f87634ba7b2db408e24fa9dd9590354b421ba024f0467992a",
  "mined_height": 372858,
  "mined_header_hash": "4216e29bbd79035af314fb64b48999295ff2431aaf76c7b299dde71b3753bbba",
  "mined_timestamp": 1765289952,
  "created_at": "2025-12-09T14:17:39Z",
  "updated_at": "2025-12-09T14:35:19Z"
}

What process can a PR reviewer use to test or verify this change?

Breaking Changes

• None
• Requires data directory on base node to be deleted
• Requires hard fork
• Other - Please specify

[gemini-code-assist]

Summary of Changes

Hello @martinserts, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new capability to the payment processor's API, enabling users to search for specific payments using their unique payment reference (payref). This feature is supported by a new database index on the payref column, ensuring efficient data retrieval, and integrates seamlessly into the existing API structure with appropriate error handling and documentation.

Highlights

• New API Endpoint: A new GET API endpoint /v1/payments/ref/{payref} has been introduced, allowing users to search for payments using their unique payref.
• Database Index for Performance: A new SQL migration adds an index on the payref column in the payments table, significantly optimizing the lookup performance for the new API endpoint.
• Enhanced Payment Retrieval Logic: A new database function get_by_payref_with_batch_info was implemented to efficiently retrieve payment details, including associated batch information, based on the provided payref.

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[gemini-code-assist]

Code Review

This pull request introduces a new API endpoint to search for payments using payref, which is a valuable addition. The implementation is sound, including a database migration to add a necessary index for performance. My primary feedback concerns an opportunity to improve code maintainability by addressing duplicated code in the database access layer. A new function is nearly identical to an existing one, and I've provided a suggestion to refactor this by extracting the common logic.