Fix mobile nav: tapping Episodes/Studies opens submenu instead of navigating, larger caret, scrollable open menu; v2.45.1

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/App.css

@@ -13275,7 +13275,20 @@ a.study-track-card:hover {
   }
 
   .header-nav--open {
-    max-height: 660px;
+    max-height: calc(100dvh - var(--site-header-h, 64px));
+    overflow-y: auto;
+    -webkit-overflow-scrolling: touch;
+  }
+
+  .nav-dropdown-label {
+    cursor: pointer;
+  }
+
+  .nav-dropdown-caret {
+    min-width: 44px;
+    min-height: 44px;
+    margin: -0.8rem 0;
+    font-size: 0.9em;
   }
 
   .nav-dropdown-trigger {