Revert SCSS @use to @import for legacy GitHub Pages compatibility

GitHub Pages legacy build uses libsass via jekyll-sass-converter 1.x,
which does not support the @use directive. Restore @import so the
production build does not fail. Tracking proper migration to a GitHub
Actions deploy workflow in a follow-up issue.

Author: mmcky

assets/main.scss

@@ -5,8 +5,8 @@
 # v2.0 - Redesign
 --------------------------------------------------------------*/
 
-@use 'misc';
-@use 'timeline';
+@import 'misc';
+@import 'timeline';
 @import url('https://fonts.googleapis.com/css2?family=Exo+2:wght@200;400&family=Roboto:wght@400;700&display=swap');
 $font-brand: 'Exo 2', sans-serif;
 $font-main: 'Roboto', sans-serif;