[Docs] Reorganize folders and sidebar in Docs

### Issue Type

Documentation Improvement

### Description

Looking for input on reorganizing the Docs sidebar and folders. (Contributing not to be changed)

In small PRs, sections will get fixed/added and this will also fix #6188

Adding a Quick Start Guide will be part of the project that will fix [#6190](https://github.com/actualbudget/actual/issues/6190)

Screenshots of sidebar:

### Documentation URL

_No response_

### Documentation Category

_No response_

### Expected/Desired Content

_No response_

### Screenshots or Examples

```bash
See above.
```

Start by reading the current Docs sidebar and folder structure and compare it with the screenshots in the issue. The issue says Contributing should not change and that work should be split into small PRs, but it asks for input rather than naming exact files or a final structure. Done would require maintainer agreement on the reorganized docs sections.

Scritto dal modello di indicizzazione a partire dal testo della issue.