Create 3 missing service READMEs (api_gateway, data_acquisition_service,
trading_agent_service). Create bin/fxt/README.md. Create
testing/service-integration/README.md. Update existing service and testing
READMEs to standard template. Delete 4 subdirectory READMEs from
testing/integration/ and testing/e2e/.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
