Add dark/light theme support

[MDJAVEED7]

This PR introduces a theme toggle feature that allows users to switch between light and dark modes across the website.

🔧 Key Changes:
Added two CSS files:

theme-dark.css

theme-light.css

Integrated a theme toggle button in the top navigation bar

Saved the selected theme using localStorage so it persists across sessions

Updated default.html to dynamically load the selected theme on page load

🧪 Tested on:
Desktop (Chrome, Firefox)

Mobile responsive check

Theme toggle works across all pages and persists reloads

📌 Notes:
Let me know if you'd like the theme colors tweaked or the toggle placed differently.

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[rspier]

Thanks Mohammed. Can you re-push without the indentation changes?

[MDJAVEED7]

i cant able to understand by means of indentation

[rspier]

Please rebase these changes against head, which should fix markdownlint, and merge the changes to fix the indentation from #131 in.

There shouldn't be whitespace only changes like this:

[MDJAVEED7]

Please check one I have edited it

[rspier]

There are still a ton of whitespace changes.

Your editor appears to be changing it from 4 space indent to 2 space indent, and re-wrapping the entire file.

Please only make the targeted changes needed to implement dark/light theme support.