ui: use hidden state for shell dropdowns

apps/ui/html/stream-sessions.html

@@ -23,7 +23,7 @@
         <span class="ws-current-name" id="ws-current-name">workspace</span>
         <svg width="11" height="11" viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M4 6l4 4 4-4"/></svg>
       </button>
-      <div class="ws-dropdown" id="ws-dropdown" style="display:none">
+      <div class="ws-dropdown" id="ws-dropdown" hidden>
         <div class="ws-dropdown-label" data-i18n="nav.workspaces">Your workspaces</div>
         <div id="ws-dropdown-list"></div>
         <div class="ws-dropdown-footer">
@@ -58,7 +58,7 @@
     </div>
   </nav>
 
-  <div class="mobile-nav">
+  <div class="mobile-nav" hidden>
     <a href="/" class="mobile-nav-link" data-i18n="nav.operations">Operations</a>
     <a href="/agents" class="mobile-nav-link" data-i18n="nav.agents">Agents</a>
     <a href="/api-keys" class="mobile-nav-link" data-i18n="nav.apikeys">API Keys</a>