feat: collapsible sidebar groups with favorites + chat visibility toggle

- Sidebar: collapsible groups (Основное/Цены/Сервис/Управление/Настройки/Разработчикам) with chevron headers, state persisted in localStorage 'sidebarGroups'
- Sidebar: Избранное group at top, star icon on nav item hover to add/remove favorites, stored in localStorage 'sidebarFavorites'
- Sidebar: active route auto-opens its group on navigation
- SettingsPage: 'Скрыть чат' toggle in Внешний вид section, stored in localStorage 'chatHidden'
- AppLayout: conditionally renders ChatWidget based on chatHidden, listens for storage events for reactive updates

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/layouts/AppLayout.tsx

@@ -1,5 +1,5 @@
 import { Outlet, Navigate } from 'react-router-dom'
-import { useState } from 'react'
+import { useState, useEffect } from 'react'
 import { Sidebar } from '../components/layout/Sidebar'
 import { Topbar } from '../components/layout/Topbar'
 import { ChatWidget } from '../components/chat/ChatWidget'
@@ -8,6 +8,17 @@ import { useAuth } from '../contexts/AuthContext'
 export function AppLayout() {
   const { user } = useAuth()
   const [sidebarOpen, setSidebarOpen] = useState(false)
+  const [chatHidden, setChatHidden] = useState(
+    () => localStorage.getItem('chatHidden') === 'true',
+  )
+
+  useEffect(() => {
+    const handleStorage = () => {
+      setChatHidden(localStorage.getItem('chatHidden') === 'true')
+    }
+    window.addEventListener('storage', handleStorage)
+    return () => window.removeEventListener('storage', handleStorage)
+  }, [])
 
   if (!user) return <Navigate to="/login" replace />
 
@@ -22,7 +33,7 @@ export function AppLayout() {
         </main>
       </div>
 
-      <ChatWidget />
+      {!chatHidden && <ChatWidget />}
     </div>
   )
 }