Build an end-to-end integration test harness for the full send/swap flow

[chillwur]

Summary

Individual services get unit/integration tests in their own issues, but nothing exercises the full path — inbound webhook payload in, on-chain testnet transaction out — as a single scenario. Build that harness as the MVP's release-readiness gate.

Description

Build a test harness that spins up the backend against real local Postgres/Redis (via the docker-compose infra) and Stellar testnet, posts a simulated WhatsApp webhook payload for a full send (including the confirm reply), and asserts a real testnet transaction lands with the expected effect.

Cover the equivalent full path for swap and for deploy + contract transfer.

Wire this as a distinct CI job (likely slower and testnet-dependent, so probably not on every PR — decide and document the trigger: nightly, pre-release tag, or manual).

This is the natural 'is the MVP actually done' checkpoint — treat it as validating the combined output of the payment, swap, and contract-deployment issues.

Deliverables

• E2E harness covering send, swap, and deploy+transfer scenarios against testnet
• CI job wiring with a documented trigger policy

Dependencies

• Depends on Implement payment signing and submission via Horizon #36
• Depends on Implement swap execution via pathPaymentStrictSend #38
• Depends on Implement contract deployment automation service #40
• Depends on Implement transaction status tracking with Horizon polling and retries #45