My existing Flutter codebase already builds and runs, but it now needs both extra functionality and a polish pass. The tasks are straightforward: • Add user authentication that supports secure sign-in and keeps sessions persistent across both Android and iOS. • Wire up in-app purchases so that users can buy consumables as well as subscriptions inside the app. • Enable push notifications, ideally through Firebase Cloud Messaging, and show them reliably when the app is in foreground, background, or killed state. • Resolve performance slow-downs (notably long startup times and sluggish list scrolling) and fix the UI glitches that cause occasional mis-alignment and flicker on some screens. I will provide the current Git repo and a brief walkthrough of the architecture as soon as we start. Once the work is done I need: 1. Updated source with clean, well-commented commits. 2. Test builds (APK & IPA) demonstrating every new feature. 3. A short changelog describing the optimisations and UI fixes. Everything should compile cleanly with the latest stable Flutter SDK and run identically on Android and iOS.