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/04-interactive/_scroll-behavior.css

@@ -190,7 +190,7 @@
         left: calc(50% - 55px) !important; /* Third button */
     }
 
-    /* Theme switcher button - fourth position (defined in color-theme.css) */
+    /* Theme switcher button - fourth position (defined in _themes.css) */
     /* left: calc(50% + 5px) !important; */
 
     .info-button {
@@ -219,7 +219,7 @@
         left: calc(50% - 85px) !important; /* Second button */
     }
 
-    /* Theme switcher on mobile - third position (see color-theme.css for override) */
+    /* Theme switcher on mobile - third position (see _themes.css for override) */
 
     .is-mobile-device .info-button {
         left: calc(50% + 35px) !important; /* Fourth button */