refactor: Clean up CSS structure and separate print.css

- Delete orphaned CSS files (color-theme.css, logo-toggle.css,
  skeleton.css, main.new.css) - replaced by modular equivalents
- Delete 08-contexts/_print.css - wrongly created during modularization
- Remove 08-contexts folder (now empty)
- Add print.css as standalone with media="print" in HTML
- Update stale comments referencing old file names
- Remove _print.css import from main.css

print.css remains standalone and will NOT be bundled, as it's a
special case loaded only when printing (media="print").

static/css/01-foundation/_variables.css

@@ -13,7 +13,7 @@
   --accent-blue: #0066cc;
   --border-gray: #dddddd;
 
-  /* Theme System - These get overridden by color-theme.css */
+  /* Theme System - These get overridden by _themes.css */
   /* Page Background */
   --page-bg: #d6d6d6;