FCE-1596: Docs restructure

[MiloszFilimowski]

Description

There is a lot to read here so I guess this PR will take a long time to review...
I welcome any of your suggestions and changes. We can treat it as a draft to work on.

What's new?

• Docs are restructured based on this guide: https://diataxis.fr/
• Much of the existing content just orgnized into a diffrent place
• There is also a lot of new LLM generated content. I tried to review the changes, especially the tutorials and examples if they work and they do as of 02.07.2025. There are also some new LLM generated pages in Concepts sections. I tried to make them more verbose and more pleasing to read and I think this was achived but there might be some LLM bullshit I might've missed.
• Replaced markdown-spellcheck with https://cspell.org/ because it has support for MDX. I just couldn't get the old lib to work with mdx comments, and cspell works great.

[linear]

FCE-1596 Plan the docs restructure

[PiotrWodecki]

part 2 out of 3