Align RDMkit styling and dependencies with ELIXIR Toolkit theme main

[bedroesb]

• Update RDMkit theme overrides for the current ELIXIR Toolkit theme main branch
• Replace obsolete Font Awesome-based search/news/event overrides with the Lucide selectors used by theme main
• Keep RDMkit custom SVG icon styling for search, news, and event metadata
• Prevent news/event metadata such as dates and PR links from wrapping awkwardly
• Move top navigation, sidebar active state, nav card arrow, metadata, and footer styling to the current Sass variable names
• Remove obsolete theme settings and no-longer-used custom Sass variables
• Align the Gemfile dependency constraints with the ELIXIR Toolkit theme main Gemfile

[bedroesb]

You might have noticed that certain stylistic things are broken in our deployment. This should fix it

[bedroesb]

I will merge this to prevent the broken state of the to-nav bar: