feat: add neo style radio input and introduce two more styles

[tim0-12432]

• Introduced two more neo styles: black logo and darkened background
• Changed the symbol only switch to an input that supports more different styles

In the screenshot, you can see the new input with the darkened background style selected.

I liked the idea of using images of examples using the styles instead of just text or smth.
Maybe we can change this later to show an exact preview of the selected icon, but performance idk...

As a reference for value settings for adjusting the background gradient, I used this Elgato ad video: https://res.cloudinary.com/elgato-pwa/video/upload/v1721061030/legacy/templateTextImageSliderView/uqecjsl7s7yunwutlnam.mp4

But of course, you can adjust the settings further in NeoIconGenerator as you like.

The default neo style is white logo as before.

Closes #294

[sebinside]

Wow, really great improvements! Looking forward to having this in the next release, thank you!