Cross-Platform Stock Trading App

I want to build a multi-broker, multi-user SaaS platform that delivers a consistent and seamless stock trading experience across Android, iPhone, Windows, and macOS using a single codebase. The core workflow is straightforward: the user signs in, views live market data, manages positions, and executes trades—all without ever leaving the app.
Phase One: SaaS Core + Broker Integration + Order Execution
Key functions to build:
• Real-time stock price streaming for instant market quote updates.
• A dashboard to track positions, average cost, and P/L, along with an advanced order page capable of handling various order types like target stop-loss and trailing stop-loss.
• Buy, sell, and order-history screens integrated with brokerage or mock-trading APIs for live execution.

Security and Sign-in
The app must feature traditional email-and-password login, biometric unlock (Face ID/Touch ID or Android equivalents), and secure token-based sessions so users don't have to re-enter credentials every time they open the app.

Platform Approach
[See Screenshot]

Deliverables =

1. Source code with a clean project structure and build instructions. 2. Compiled builds ready for submission to the Google Play Store and Apple App Store, plus installers for Windows and macOS.
3. Separate API keys and environment variables for easy handover. 4. A brief setup document and a video walkthrough demonstrating real-time data, portfolio updates, and demo trades.
Please provide details of trading or fintech apps you have previously developed—code quality and reliability are paramount to me.