* Improve layout of documentation page and add search feature
Closes https://github.com/FreshRSS/FreshRSS/issues/7915, https://github.com/FreshRSS/FreshRSS/issues/5325
Also: anchor headings and fix building site locally
* Further improvements
* Set color of hyperlinks
* Consistent styling of close aside button across devices
* Mobile layout 600px -> 1200px
* Add suffix to docs `<title>`
* Note: titles of pages probably need to be improved, since currently they are just derived from the names of the first heading on every page
* Add favicon
* Improve font
* Try to fix favicon not loading correctly on GH pages
* Use local font
* Attempt to fix GH pages
* Final improvements
* Copy to clipboard button
* Support for nojs search
* Dark mode
* Load search.json (200KB json) only on search input focus
* Keep scroll state of sidebar across navigations
* Clickable images and CSP
CSP so we avoid hotlinking resources and clickable images are useful for zooming on mobile for example
* Fix typos
* Disable Dark Reader extension if dark mode CSS is loaded
* Support internationalisation (via language dropdown)
* Add Gemfile.lock
* Make CI build work with the custom plugin
* Make menus closable with Esc
* Fix typos CI
* Suggestions
* Use `ruby/setup-ruby` action in workflow for installing and caching gems.
* Run build only when there are changes to `docs/`
See: https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows?versionId=free-pro-team%40latest&productId=actions#running-your-workflow-only-when-a-push-to-specific-branches-occurs
* Change font to `Open Sans`
* Increase line height
* Fix Liquid syntax error
