feat(frontend): restore Zibll-like global search panel

Render full search overlay with types/history/suggestions for tabbar
and desktop header toggle. Open panel on all viewports (not mobile-only)
and wire data-toggle-class/.navbar-search compatibility hooks.

assets/css/frontend/footer/part-3.css

@@ -301,3 +301,44 @@ html.dark .footer-tabbar {
 .site-footer--compact .site-footer__brand {
     flex: 1 1 100%;
 }
+
+
+/* Full-viewport search panel open state (desktop + mobile) */
+.tabbar-search-overlay[hidden] {
+    display: none !important;
+}
+.tabbar-search-overlay.is-open,
+.tabbar-search-overlay.show:not([hidden]) {
+    display: flex;
+}
+.tabbar-search-overlay__dialog {
+    max-width: 720px;
+    margin: 0 auto;
+}
+@media (min-width: 768px) {
+    .tabbar-search-overlay {
+        align-items: flex-start;
+        padding-top: 8vh;
+        background: rgba(15, 23, 42, 0.45);
+    }
+    .tabbar-search-overlay__dialog {
+        min-height: auto;
+        max-height: min(84vh, 860px);
+        overflow: auto;
+        border-radius: 20px;
+        box-shadow: var(--shadow-lg, 0 20px 50px rgba(15, 23, 42, 0.22));
+    }
+    .nav-searchbox--desktop {
+        display: none;
+    }
+    .main-search-btn.nav-search-toggle {
+        display: inline-flex;
+        align-items: center;
+        justify-content: center;
+    }
+}
+@media (max-width: 767.98px) {
+    .main-search-btn.nav-search-toggle {
+        display: none;
+    }
+}