feat: add initial implementation of Kitchen CRM with authentication and dashboard features

- Create global styles and theme management
- Implement app shell layout with sidebar navigation
- Add authentication layout and pages for login and registration
- Develop dashboard page with placeholder content
- Introduce routing guards for guest-only and authenticated routes
- Set up Zustand for state management of authentication and theme
- Create API types and structures for CRM entities
- Configure Vite with PWA support and Tailwind CSS

frontend/src/components/system/app-loading.tsx

@@ -0,0 +1,8 @@
+export const AppLoading = () => (
+  <div className="flex min-h-screen items-center justify-center bg-background text-foreground">
+    <div className="space-y-3 text-center">
+      <div className="mx-auto h-10 w-10 animate-spin rounded-full border-2 border-primary border-t-transparent" />
+      <p className="text-sm text-muted-foreground">Загружаем Kitchen CRM…</p>
+    </div>
+  </div>
+)