feat: support Artalk comment system

[powerfullz]

This pull request introduces support for the Artalk comment system, including configuration, styling, and dynamic loading of the Artalk widget. The changes are grouped into configuration updates, asset and style integration, and widget initialization.

Artalk comment system integration:

• Added Artalk configuration options (serverUrl, site) to the params.toml config file, enabling site owners to set up Artalk as a comment provider.

Styling and assets:

• Created a new SCSS partial (artalk.scss) with custom styles for the Artalk widget, including theme variables and responsive design, and imported relevant mixins and breakpoints.
• Integrated the compiled and minified Artalk SCSS into the HTML partial, ensuring consistent styling with the site's theme.

Widget initialization and dynamic loading:

• Implemented dynamic loading of Artalk's CSS and JS from CDN in the artalk.html partial, initializing the widget with page-specific parameters and supporting dark mode.
• Added event listener to update Artalk's theme in response to color scheme changes, maintaining visual consistency across theme switches.