Update link styling: darker gray-blue color and remove default underline

[bhouston]

Update Link Styling: Darker Gray-Blue Color and Remove Default Underline

Description

The current link styling in the documentation site uses a blue color (#0066cc) with underlines by default. This PR will:

1. Change the link color to a darker gray-blue shade
2. Remove the default underline from links (they will still underline on hover)

Why

• A darker gray-blue will improve readability and provide a more subtle, professional appearance
• Removing the default underline will create a cleaner look while maintaining accessibility standards with hover underlines

Implementation Plan

• Update the CSS variables in src/css/custom.css:
  • Modify --ifm-link-color to a darker gray-blue shade
  • Modify --ifm-link-hover-color to a slightly darker version of the new color
  • Change --ifm-link-decoration from underline to none