Auto-close download platform selection menu

[mgiannopoulos24]

Summary

The download platform selection menu now automatically closes after a user selects a target platform for download, improving user experience and aligning with common UI patterns.

Related issue

Closes #270

Changes

• Added assets/javascript/download-button.js to handle auto-closing functionality
• Updated _layouts/page.html to include the new script

How it works

The script listens for change events on platform radio buttons and automatically unchecks the menu visibility checkbox, closing the menu immediately after selection.

Testing

• Select any platform (Windows, macOS, Linux) → menu closes automatically
• Works correctly with multiple download buttons on the same page

[mgiannopoulos24]

I also wanted to implement #253 but I wasn't so sure on how to generate the icon fonts. The alternative way would be to use the SVG as code. I would recommend using this SVG.