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/pages/SettingsPage.tsx

@@ -51,6 +51,18 @@ export function SettingsPage() {
     })
   }
 
+  const [chatHidden, setChatHidden] = useState(
+    () => localStorage.getItem('chatHidden') === 'true',
+  )
+  const toggleChatHidden = () => {
+    setChatHidden(v => {
+      const next = !v
+      localStorage.setItem('chatHidden', String(next))
+      window.dispatchEvent(new Event('storage'))
+      return next
+    })
+  }
+
   const [form, setForm] = useState({
     name: '',
     address: '',
@@ -588,6 +600,18 @@ export function SettingsPage() {
                     <Toggle on={calendarCompact} onChange={toggleCalendarCompact} />
                   </div>
                 </div>
+
+                {/* Chat widget visibility */}
+                <div className="pt-3 border-t border-slate-100 dark:border-slate-700">
+                  <p className="text-sm font-medium text-slate-700 dark:text-slate-300 mb-2">Чат-виджет</p>
+                  <div className="flex items-center justify-between p-3 rounded-lg bg-slate-50 dark:bg-slate-700/40">
+                    <div>
+                      <p className="text-sm font-medium text-slate-900 dark:text-slate-100">Скрыть чат</p>
+                      <p className="text-xs text-slate-500 dark:text-slate-400">Убрать кнопку чата из интерфейса</p>
+                    </div>
+                    <Toggle on={chatHidden} onChange={toggleChatHidden} />
+                  </div>
+                </div>
               </div>
             </>
           )}