ARC-134 refactor SCSS

[rshiggin]

Moved active SCSS to top-level app/assets/stylesheets. To aid development, split SCSS into separate compiled CSS files:

1. default Bootstrap 5 bootstrap.css
2. custom, mlibrary-specific CSS now compiles into application.css < all additional custom and updated CSS should be imported with application.scss file.

Modified SCSS pipeline in layouts/application.html.erb, initializers/assets.rb, `package.json'

[rshiggin]

CI failures

• Lint issues in helpers/dul_arclight_helper.rb, helpers/contact_link_helper.rb, helpers/catalog_helper.rb
• Update brakeman gem 8.0.4 > 8.0.5

[ssciolla]

LGTM