Flutter Basic Calculator App

I need a straightforward, reliable calculator built with Dart + Flutter that runs smoothly on Android and follows Google’s Material Design guidelines. The scope is intentionally simple—think classic four-function math (add, subtract, multiply, divide) with a clean, responsive UI that scales well across common phone screen sizes.

Here’s what will make the project a success for me:
• A single-screen Material Design interface with clearly labeled buttons and an easy-to-read display
• Accurate handling of basic arithmetic operations, including chaining calculations and a clear/reset function
• Well-structured Flutter code, free of unnecessary packages, so I can continue maintaining it after delivery
• An installable APK plus the full Dart/Flutter source in a Git repository

If you include concise in-code comments and a brief README on how to build or tweak the project, that will be perfect.