Fix: Respect user's browser theme preference on initial load

[milinddethe15]

What

Set the default color scheme to "auto" to respect the user's browser/system theme preference when first loading the site.

Changes

• Updated MantineProvider to use defaultColorScheme="auto"
• Updated ColorSchemeScript to use defaultColorScheme="auto"

Before

Site always loaded in light mode regardless of user's browser preference.

After

Site now loads with the user's preferred theme (dark/light) based on their browser/system settings, while maintaining the ability to manually override via the theme selector.