fix: restrict hover styles to pointer devices via @custom-variant

Prevents hover state from sticking on touch screens by scoping
hover to actual hover-capable devices.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/css/main.css

@@ -4,6 +4,8 @@
 @source "../../content/**/*.md";
 @source "../../assets/js/**/*.js";
 
+@custom-variant hover (&:hover);
+
 /* ── Design tokens ─────────────────────────────────────────────────────────── */
 @theme {
   /* Core palette — exact match to design */