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.

[vishesh92]

Personally I prefer dark mode for pages and I always have it on by default on my system.
There are a few things which might need fixing in the UI for dark mode. e.g. images needs to have a transparent background instead of white.

I propose that we do this:

1. Add the toggle on the website. But keep the dark mode disabled by default.
2. Fix whatever we need to do from UI/UX perspective.
3. Once everything is ready, we can change the setting to pick the system settings as a default. So, if you have selected "Dark Style" at OS level, the website will show up in Dark Mode. Otherwise it will show up in light mode.
   (Browsers expose the system settings to the website which then toggles the dark mode automatically).