First draft implementation of Element Call and Widget API

[shakhzodkudratov]

Hello everyone! Thank you very much for such awesome project!

We needed Element Call part and had no success finding implementation for Flutter. So we decided to implement it on our own. Due to internal deadlines most of the code was written using Claude Code as assistant. This PR requires a good amount of reviews and polishing works. But as a Proof-of-concept work you can clone and play around with it.

What is working:

• Widget Machine
• Unencrypted calls
• Encrypted calls
• Direct Message calls
• Room/Group calls

What is not working/broken:

• Callkit requires polishing and testing from iOS side
• Cross-platform is not tested. Our target was Android and testing was only on this platform
• Push notifications are not tested

Thank you so much for your contribution to FluffyChat ❤️❤️❤️

• I have read and understood the contributing guidelines.

Pull Request has been tested on:

• Android
• iOS
• Browser (Chromium based)
• Browser (Firefox based)
• Browser (WebKit based)
• Desktop Linux
• Desktop Windows
• Desktop macOS