flutter/samples — reverse-engineered prompt

Build me a Flutter sample gallery app that feels like a friendly starting point for learning Flutter. I want one home screen where I can browse different example categories like forms, navigation, animations, Material 3 design, Cupertino style screens, maps, desktop photo search, shaders, platform features, and testing.

Each example should open into a simple runnable demo that shows the idea clearly without lots of extra complexity. Keep the code clean and easy to reuse, like official sample code. It should work as a normal Flutter app on mobile, and where it makes sense on desktop or web too.

Please include polished but simple UI, clear navigation, and short explanations inside each sample so someone can understand what they’re looking at. If a feature needs platform setup, like maps or native platform integration, add a placeholder screen with guidance instead of breaking the app.

Use current Flutter best practices, and look up current docs online if you need to.