fix(web): header dropdowns sit above the page again

Every shell child got the same z-index, so the page painted over the search
suggestions and the profile menu and swallowed their clicks: suggestions could
not be picked, and the language switch and settings item did nothing.

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

apps/web/src/widgets/AppShell.module.css

@@ -27,8 +27,10 @@
   padding-bottom: 132px;
 }
 
+/* Над контентом: выпадающие подсказки поиска и меню профиля перекрывают страницу, а не уходят под неё. */
 .top {
   grid-area: top;
+  z-index: 30;
   display: flex;
   align-items: center;
   gap: 24px;