Server-side rendering (SSR) for SEO, faster loading and social sharing

[rodja]

As written in #637 (comment), SSR would especially beneficial for SEO, faster loading and social sharing. Because #637 is focusing on static-site generation (SSR), this ticket will focus on SSR as suggested by @falkoschindler in #637 (reply in thread).

[falkoschindler]

It looks like SEO isn't as bad as expected. Google Page Speed rates SEO for nicegui.io with 100%:
https://pagespeed.web.dev/analysis/https-nicegui-io/2xzi6ku0ky
Of course, there are other deficits, which we are working on (#658). But maybe SEO is not an issue.

[evnchn]

A tough one: progress at evnchn#83