feat: Add paper theme and light theme support

- Introduced new 'paper' light theme in README.md
- Added new blog post explaining the paper theme
- Included paper theme image
- Updated theme color options to include 'paper'
- Added new CSS variables for light theme support

demoSite/content/posts/paper-a-light-theme.md

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+title = "Introducing Paper a light theme"
+date = "2025-03-12"
+author = "Mirus"
+cover = "img/paper.jpeg"
+coverCaption = "The first light theme by community member trviph"
+description = "As planned, re-Terminal got the first prebuilt light theme. Read some details in the article"
+tags=["theme", "light"]
++++
+
+## About Paper
+
+We have an issue on the [GitHub](https://github.com/mirus-ua/hugo-theme-re-terminal/issues/10) about the built-in light themes for re-Terminal Hugo Theme, and today I'm glad to introduce the very first light theme made by  [trviph](https://github.com/trviph) that is called `Paper`.
+
+You can enable it via config 
+```yaml
+[params]
+  themeColor = "paper"
+```
+
+## Tech enablers
+With the new theme we got a few handy improvements:
+- `--menu-color` a new CSS Variable
+- `assets/css/variables-light.scss` a new conditional set of variables for the light themes; you can start your very own theme with [CSS Variables](/posts/css-vars/) and better defaults if you aren't on the dark side  
+
+## Outro
+If you want to add your vision of a perfect accessible light theme, I'm gladly accept your contribution