Feature-flag, verify, and release the multichain swap MVP

[stxphxn]

Summary

Integrate the production swap-router, verify the four-network MVP as a coherent product, and release it behind a reversible feature flag.

Dependencies

• Add multi-chain market and wallet foundations for routed swaps #66
• Add the swap-router API client and provider-neutral quote model #67
• Refactor Swap for chain-aware market selection and route comparison #68
• Execute routed swaps and track destination settlement #69
• cenodev/setwise-swap-router#5

Scope

• Add a disabled-by-default production feature flag and a documented rollback path that leaves existing Setwise swaps available.
• Run unit, integration, accessibility, responsive, lint, type-check, and production-build checks.
• Exercise representative same-chain and cross-chain routes across Ethereum, BNB Chain, Base, and Robinhood Chain using disposable wallets and deliberately small amounts.
• Verify exact destination contracts against the canonical Setwise token catalog and issuer sources before each smoke route.
• Test no-liquidity, provider timeout, wrong chain, insufficient gas, rejected approval, stale quote, source revert, destination failure/partial, refund, reload/resume, and provider-disable behavior.
• Verify API CORS, production origin, rate limits, monitoring, correlation IDs, and that no API key is shipped in browser assets.
• Review external-facing issuer terminology, eligibility disclosures, route/provider disclosures, fee presentation, and risk copy; obtain the required product/legal sign-off rather than encoding assumptions.
• Record app/API commits, deployments, route IDs, transaction hashes, evidence, known limitations, and rollback steps.

Acceptance criteria

• The feature can be enabled or disabled without redeploying contracts or losing the existing Swap path.
• At least one successful same-chain and one successful cross-chain acquisition are evidenced, and every core network is exercised as source or destination where live liquidity permits.
• Negative and recovery cases are evidenced without misreporting success or leaving unexplained approvals.
• Monitoring distinguishes Setwise app errors, router errors, and upstream provider failures.
• Release notes state exact-input and explicitly selected destination market as the MVP limits.

Difficulty

High — cross-repository production acceptance with real-wallet and recovery evidence; use the strongest coding model.