Android WebView App With File Transfer

Android WebView App for EstiBill – Source Code Required
I have a fully responsive web application called EstiBill, an online estimate, quotation and invoice/billing application. The website is already complete and working. I need an Android WebView application that provides a smooth, native-app-like experience.
Main Requirements:
• Open my EstiBill web app URL inside Android WebView and keep normal navigation inside the app.
• Full support for PDF downloads. PDFs generated by my website must download correctly to the user's device with the correct PDF filename, not a random/encoded filename.
• Full support for file uploads, including camera, gallery and Android document/file picker.
• Support WhatsApp links, phone links and other external links correctly.
• JavaScript, cookies, sessions/login and local storage must work properly.
• Show a smooth loading/progress indicator while pages are loading.
• Proper offline/no-internet screen with Retry button.
• Android Back button should navigate to the previous WebView page when possible.
• When the user presses Back from the EstiBill Home/Dashboard, show a professional confirmation dialog: “Do you want to exit EstiBill?” – Yes / No, instead of immediately closing the app.
• Create a professional EstiBill splash screen using the logo/branding I provide.
• App icon and splash screen should use my supplied EstiBill logo.
• Status bar/navigation appearance should match the EstiBill blue/white branding.
• Do not add unnecessary native headers/toolbars above my website because the web app already has its own UI.
• Handle Android permissions properly and only request permissions when required.
• Target the latest Google Play Store required Android SDK/API level.
• App must compile successfully in Android Studio and be suitable for Google Play submission.
Important: This is NOT just a basic “URL to APK” conversion. PDF downloading, correct PDF filenames, file upload/camera/gallery picker, Back navigation and exit confirmation must be properly implemented and tested on a real Android device.
Deliverables:
Complete editable Android Studio source code (Java or Kotlin).
Release-ready APK.
AAB file for Google Play Store submission.
Unsigned/debug build for testing and future development.
Simple README explaining how to change the website URL, app name, logo, splash screen and theme colours.
App Name: EstiBill
Website/Web App: I will provide the live URL after hiring.
Brand Assets: EstiBill logo/app icon will be provided.
Please mention your fixed price, estimated delivery time, and examples of Android WebView applications you have previously developed. I prefer a developer who has experience with WebView PDF downloads and file uploads.