feat: add dark mode toggle

[jbampton]

This is my quick attempt at adding dark mode to our website.

With the help of Gemini. Some screen shots below:

[IvetPM]

Hey,

Good initiative to put some thinking around the website. My question would be why we actually need this?
It is a project website, it is not a personal dashboard or software, so a user can decide how it will look.
My opinion is against this for several reasons:

• The choice of colours is important for the overall UX and website usability. This is a project website, not a software solution.
• Better readability for technical content – Dark text on a white background is easier to read.
• Stronger usability & UX – Clearer hierarchy, better link visibility, improved scannability, and reduced eye strain enhance overall user experience.
• The white version supports Google’s ranking priorities – Google rewards readability, accessibility, engagement, and structured content. Light themes better support these usability signals.
• Improved accessibility & standards compliance – Easier to meet WCAG contrast requirements and modern web accessibility standards.
  This is my view. I will be happy to hear more opinions.