fix(nav): hide mobile drawer/search off-flow to kill blank band

Desktop was rendering .mobile-header / .mobile-navbar in document flow
because Bootstrap 5 has no visible-xs-block and drawer CSS only ran
inside max-width:767px. Hide drawer shell by default; only show as fixed
off-canvas on small screens. Also fix orphan CSS rules in navbar-core,
give .navbar-search position:fixed so the overlay never reserves height.

assets/css/frontend/nav/zib-navbar-core.css

@@ -50,10 +50,6 @@
     transition: 0.3s;
 }
 
-
-    margin-left: -100%;
-}
-
 .header {
     padding: 8px 20px;
     background: var(--header-bg);
@@ -252,14 +248,12 @@ body.nav-fixed .slide-header {
     z-index: 999;
     width: 100%;
     top: 0;
+    left: 0;
+    right: 0;
     -webkit-backdrop-filter: saturate(5) blur(20px);
     backdrop-filter: saturate(5) blur(20px);
 }
 
-.mobile-navbar + .fixed-body {
-    z-index: 996;
-}
-
 .navbar-top {
     margin: 0;
     border-radius: 0 !important;
@@ -385,6 +379,11 @@ badge.top,
 }
 
 .navbar-search {
+    position: fixed;
+    left: 0;
+    right: 0;
+    top: 0;
+    width: 100%;
     visibility: hidden;
     transform: translateY(-101%);
     padding: 10px 30px;
@@ -396,11 +395,13 @@ badge.top,
     z-index: 998;
     transition: all 0.5s;
     border-radius:0 0 var(--main-radius) var(--main-radius);
+    pointer-events: none;
 }
 
 .navbar-search.show {
-    visibility: unset;
+    visibility: visible;
     transform: translateY(0);
+    pointer-events: auto;
 }
 
 .navbar-top .navbar-right .sub-menu {
@@ -672,7 +673,7 @@ badge.top,
     height: 36px;
 }
 
-
+@media (min-width: 768px) {
     .container {
         width: 95%;
     }