Flutter Firebase Local Marketplace App -- 2

You are seeking a senior full-stack mobile app developer and product architect to build a NearBook-style local marketplace app. The app will allow users to rent or sell second-hand products within a 5–10 km radius. Each user will act as both buyer and seller, with a ₹1 booking fee charged before confirming bookings. The app will prioritize simplicity, trust, and proximity over complex features.

Key Features:
- User Flow: Splash screen → Phone OTP login → Allow location → Home (nearby products) → Product details → Book product (₹1 payment) → Contact seller (Call/WhatsApp).
- Core Features: Location-based product listing, Rent/Sell modes, ₹1 booking fee, direct user-to-user contact via Call/WhatsApp.
- Home Screen: Vertical list of products sorted by distance within 5–10 km radius.
- Search & Filter: Search by product name; filter by category, price, distance, and mode (Rent/Sell).
- Product Details Screen: Displays product images, prices, condition, description, distance from user, and seller details after booking.
- Add Product Flow: Upload images, select category, set Rent/Sell prices, auto-fetch location, and publish.

Tech Stack:
- Frontend: Flutter
- Backend: Firebase (Auth with Phone OTP, Firestore for database, Storage for images)
- Location: Geolocator for fetching user location and calculating distances
- Payments: Razorpay (₹1 UPI payments)
- Contact: url_launcher for Call/WhatsApp

Deliverables:
1. Complete Flutter source code in an organized repository.
2. Firestore security rules and minimal indexes.
3. APK + iOS TestFlight build for testing.
4. Brief setup guide for local deployment and updates.