Revert: disable sticky header on mobile as intended

Restore position: relative on mobile so the header scrolls away
on small screens. Sticky only applies on desktop (>= 992px).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/media/css/template.css

@@ -14224,10 +14224,11 @@ fieldset>* {
 	z-index: 1020;
 }
 
-/* Sticky header on mobile — keep sticky but lower z-index to avoid overlay issues */
+/* Disable sticky on mobile — full-width header works better as static */
 @media (max-width: 991.98px) {
 	.container-header.sticky-top {
-		z-index: 1020;
+		position: relative;
+		z-index: 100;
 	}
 }