MarkdownViewer don't use my custom text color

### Description The `MarkdownViewer` component does not support custom text colour for normal markdown spans. When using a dark background theme, the markdown preview remains hard to read because the custom colour is ignored. Thanks for read. ### Steps to Reproduce 1. Use `MarkdownViewer` with a dark theme background. 2. Set a custom text colour via `MarkdownViewer` theme or `.color(...)`. ```rs MarkdownViewer::new(markdown) .padding(Gaps::new_all(8.0)) .color(theme_colors.text_primary) // Being "text_primary" // text_primary: Color::from_rgb(196, 206, 219) ``` 3. Render markdown content containing normal paragraph text. ### Expected Behavior Normal markdown text should use the custom text colour provided by the theme. The component should render readable text on dark backgrounds. ### Actual behaviour Only code spans or specific elements receive the custom colour. Regular paragraph spans keep the default colour, causing poor legibility in dark mode. ### Freya Version 0.4.0-rc.19 ### Rust Version rustc 1.95.0 (59807616e 2026-04-14) ### OS Version Windows 10 22H2 ### Additional Context ### This is my preview: <img width="1365" height="740" alt="Image" src="https://github.com/user-attachments/assets/8c459694-19f4-420d-b1e5-ba359813f35f" />