Document Flet in macOS, iOS, and Android guides #159003

I'm a maintainer of Flet, an open-source framework for building cross-platform applications in Python.

Would you be open to including Flet among the third-party tools mentioned in Python's macOS, iOS, and Android documentation?

Flet supports creating desktop, mobile, and web applications in Python and packaging them for distribution through its flet build command. It recently released version 1.0. Platform-specific documentation is available for:

• macOS
• iOS
• Android

The proposed additions would cover these files on main:

• Doc/using/mac.rst — GUI programming
• Doc/using/ios.rst — introductory guidance on app frameworks
• Platforms/Apple/iOS/README.md — introductory guidance on build tools
• Doc/using/android.rst — Adding Python to an Android app

These sections already point readers toward third-party projects that simplify GUI development or mobile packaging. Including Flet would help readers discover another available option.

I'm proposing brief additions consistent with the existing entries, retaining the current tools. For example, the macOS entry could read:

Flet: A framework for building cross-platform desktop, mobile, and web applications in Python.

I'd be happy to submit a documentation PR. Feedback on whether these are appropriate locations, and on the wording or scope, would be welcome.

Thank you!

CC @freakboy3742, @mhsmith