Project Overview: I am looking for an experienced Flutter developer to build a simple Proof of Concept (POC) app. The goal of this app is to serve as a learning tool/template for my main project (a personal assistant). I need to understand how to implement high-priority notifications that mimic an incoming phone call (ringing, full-screen intent) triggered by a backend event. Target Platform: Android (APK delivery required). Core User Flow: Installation & Setup: User installs the APK. On first launch, the app requests necessary permissions (Notifications, Full-Screen Intent, Overlay permissions if required). Main Interface: A simple screen with two buttons: Button 1: "Schedule Call (30s)": When clicked, it starts a 30-second timer. (Note: While I want to learn backend integration, for this simple demo, a local scheduler is fine unless you can easily set up a dummy Firebase trigger). Button 2: "Hangup/Exit": Closes the app/minimizes it. The Notification (Crucial Feature): After 30 seconds, the device receives the notification. Scenario A (Phone Locked/Asleep): The notification must appear Full Screen (like a customized incoming call UI) with "Accept" and "Decline" buttons. Scenario B (Phone Unlocked): A high-priority heads-up notification (banner) appears at the top with "Accept" and "Decline" action buttons. Interaction: If "Decline" is pressed: The notification/ringing stops and dismisses. If "Accept" is pressed: The app opens/comes to the foreground and displays a specific text message: "Hi, this is your notification." Technical Requirements: Framework: Flutter. Notifications: Must utilize standard plugins (e.g., flutter_local_notifications, awesome_notifications, or firebase_messaging). "Ringing" Behavior: The notification must use High Priority channels and Full-Screen Intent (Android) to wake the screen. Code Quality: Since this is for me to learn, the code must be heavily commented. I need to clearly see where the notification channel is created, how the payload is handled, and how the background listener is set up. Deliverables: Complete Source Code (zipped or GitHub link). Compiled .apk file for testing. A short text file or README explaining: Which libraries were used. How to change the icon/sound of the notification. Any specific AndroidManifest settings used (e.g., USE_FULL_SCREEN_INTENT).