Backend & Database Setup for React/TypeScript PWA (Carpooling App)

I am looking for an experienced Fullstack/Backend developer to build the server-side architecture, database, and platform integrations for a ready-made mobile app/PWA prototype called "PODWÓZKA" (a smart urban carpooling application). The entire visual layer (frontend), screen layouts, user interface (passenger/driver views), and live map animations are already fully coded and functional in React/Vite/TypeScript (generated and hosted via Bolt.new). The project language is Polish, but all frontend texts are already in place, so no translation or content writing is required. Your job is strictly focused on bringing the existing frontend to life by connecting the backend logic. Detailed Scope of Work: 1. Database & Authentication: Set up a secure database (Supabase / PostgreSQL preferred) and user authentication (Google Auth, Facebook Auth, Email). The user profile must distinguish between "Driver" (inputs car make, color, license plate) and "Passenger". Implement a rating (1-5 stars) and review system within the user profiles. 2. Geolocation & Initial Route Setup: Configure the backend to handle the first test route in Poland (Gdańsk region). The system should pair drivers and passengers with matching commute times based on GPS coordinates using free OpenStreetMap data. Pickup points should display public commuter hubs (Meeting Points). 3. Safety Logic (Karos / BlaBlaCar Daily model): Implement a 4-digit PIN verification code generated on the passenger's screen, which the driver must enter and confirm upon pickup to log the start of the trip. Add logic for the "Share live trip" button (generating a temporary GPS token for real-time tracking). 4. Ad Monetization (Google AdMob): Integrate the official Google AdMob SDK into the designated placeholder banner slots at the bottom of the screens for free-tier users. 5. Premium Subscription System: Integrate native in-app payment systems (Google Play Store Billing and Apple In-App Purchases) for the "Go Premium for 4.99 PLN" button. Purchasing Premium must permanently update the user's status in the database and hide AdMob ads. 6. Payment Status Display: Display a fixed text notice to the passenger showing the suggested fuel contribution (flat 4.00 PLN, paid directly to the driver via cash or instant mobile transfer. The app does not process this peer-to-peer payment; there is no in-app wallet). Requirements: - Access to the Bolt.new source code and live preview will be shared upon request. - Payment will be released via Upwork Escrow milestone system upon successful testing on a mobile device. - Please provide your fixed price estimate and expected timeline for delivery.