Add main menu page with role-based modules (#7)

- `/` is now the main menu; orders/receipts page moved to `/receipts`
- Module registry (features/menu/modules.ts) drives both the menu tiles
  and route guards (ModuleRoute); admin sees every module
- Menu: module search with Ctrl+K, profile with logout, responsive grid,
  palette matching the login page
- «← Головне меню» link on receipts and cash registers pages;
  «Каси» moved from the receipts toolbar into the menu

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

frontend/src/features/menu/ModuleRoute.tsx

@@ -0,0 +1,11 @@
+import { Navigate, Outlet } from 'react-router-dom'
+
+import { useAuth } from '@/features/auth/useAuth'
+import { canAccess, getModule } from '@/features/menu/modules'
+
+/** Пускает в модуль только роли из реестра; остальных возвращает в главное меню. */
+export function ModuleRoute({ moduleId }: { moduleId: string }) {
+  const { user } = useAuth()
+  if (!canAccess(user, getModule(moduleId).roles)) return <Navigate to="/" replace />
+  return <Outlet />
+}