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.