Fix link styling and remove dark mode switcher

[bhouston]

Fix Link Styling and Remove Dark Mode Switcher

This PR addresses two issues:

1. Make Links Visually Distinguishable (Fixes #30)

• Changed link color to blue (#0066cc) from black
• Added underlines to links
• Updated primary color scheme to use blue tones instead of grayscale

2. Remove Dark Mode and Mode Switcher (Fixes #31)

• Fixed the Docusaurus configuration to properly disable dark mode
• Consolidated the duplicate themeConfig objects in the config file
• Ensured the colorMode settings are correctly placed in the configuration structure

Testing

• Built the project successfully
• Verified links are now blue and underlined
• Confirmed dark mode switcher is no longer present in the navigation bar

These changes improve user experience by making clickable elements more obvious and reduce testing overhead by removing the dark mode option.