Integrate the website header in the Documentation sections

[miohtama]

Currently, documentation comes from a separate statically generated site using Sphinx documentation tool. To give a more professional appearance, the documentation theming should be better integrated with the website. The first step would be to the website header (nav bar) appear on the documentation pages as it appears on the website.

• The documentation will be served as a statically generated site short-medium term
• Explore the options how to get nav bar from an (external) Svelte site to appearing a static HTML

For example:

• Create a route that only renders the nav bar
• This navbar is fetched to external HTML as a AJAX request and then cached in localStorage (the nav bar rarely changes so long cache times are ok)

The documentation is generated here:

https://github.com/tradingstrategy-ai/client/tree/master/docs

The main Sphinx template is here (uses Jinja):

https://github.com/tradingstrategy-ai/client/blob/master/docs/source/_templates/layout.html