add transaction lifecycle service

[Jayking40]

[Backend] Feature: Transaction Service

Summary

Implemented a transaction lifecycle service for the backend so transaction writes are validated consistently, transaction history can be queried with richer filters, and merchants can manage refunds, reconciliation, and reporting from the same transaction domain model.

Changes

• Added a dedicated transaction service layer to centralize validation, Stellar verification, history filtering, merchant-scoped queries, refunds, reconciliation, and reporting logic.
• Extended transaction persistence to support lifecycle fields such as status, reconciliation timestamps, refund linkage, refund reasons, and metadata while preserving existing transaction flows.
• Expanded the transactions API with merchant history, reporting, refund, and reconciliation endpoints, and updated tests to cover the new lifecycle behaviour and fallback paths.

Testing

• Unit tests written for:

• Transaction service validation and lifecycle flows

• Transaction routes and user history route behaviour

• Repository round-trip, nullability, merchant isolation, and Horizon fallback cases

• Edge cases covered:

• Duplicate transaction recording

• Invalid wallet addresses, invalid amounts, and reversed date ranges

• Refund ownership checks and invalid refund targets

• Horizon failure with database fallback

• Merchant-scoped filtering and reconciliation/report filters

• Manual testing steps (if applicable):

• Ran targeted backend Jest suites for the transaction service, routes, repositories, property tests, and Horizon fallback flow

• Ran focused ESLint checks on the touched transaction files

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Closes #352

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[milah-247]

@Jayking40 you pushed from main

[milah-247]

You have conflict

[milah-247]

@Jayking40 you're pushing from main not branch

[milah-247]

Push from your branch not main