Build MXN→USDT Crypto Trading Desk on Bitso API

We're a LATAM cross-border payments company building v1 of a crypto trading desk: a secure web app where a single institutional customer funds an MXN balance via SPEI and buys USDT, executing against Bitso with our configured spread. A complete PRD is attached — please read it before bidding. ⏱ HARD REQUIREMENT: a working v1 must be deployed to PRODUCTION within 5 days of kickoff. Senior-only sprint. Core buy flow live in production first; the full non-functional scope in the PRD is the committed target. UI/UX design runs in parallel; brand polish is a fast-follow. WHAT YOU'LL BUILD (full detail in the attached RFP): - Real-time balance (MXN/USDT), SPEI deposit instructions, and a best-execution buy — depth-aware across Bitso's order book (ORDERS) and BRFQ/OTC (RFQ), routing to the better price, filling across book levels, with VWAP costing and our spread. - On-chain tx hash capture for each USDT credit (from the Bitso API), order confirmation and history, operator oversight/margin view, and an immutable audit trail (four-eyes on sensitive actions). - Multi-user with RBAC + MFA; server-only Bitso key boundary; near-real-time UX (SSE + Bitso WebSocket); managed PaaS; GitHub CI/CD; automated tests; observability. - UI/UX design to our brand guide (attached) — minimal, low-fi but unmistakably on-brand, using our typography — delivered with editable source files (Figma preferred). TWO WAYS TO DELIVER (your choice — justify it in your proposal): - Option A — adapt a mature open-source trading/exchange platform. - Option B — greenfield on Remix 3 + TypeScript. MUST-HAVES: - Track record shipping fintech/crypto fast, ideally against an exchange trading API (Bitso a strong plus). - Full-stack TypeScript/Node; real-time (WebSocket/SSE); Postgres; CI/CD; production deployment on managed PaaS (AWS/GCP/Supabase/Upsun or equivalent). - Design capability to deliver brand-compliant screens + Figma source. - Start immediately, work intensively across the 5-day window, strong async comms, Americas time-zone overlap. DELIVERABLES: working v1 in production, editable design source (Figma), source in our GitHub, infrastructure-as-code, tests, observability, and local-setup docs — all per the RFP. ONGOING MAINTENANCE: we also want ~5 hours/month of ongoing maintenance and support after launch, at an agreed hourly rate. This runs as a separate hourly contract post-handover — please state your maintenance hourly rate in your proposal. BUDGET: Fixed price for the build. Quote your all-in build bid plus a brief milestone plan (target: sandbox core → production in 5 days), and separately your monthly maintenance hourly rate.