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/postcss.config.js

@@ -0,0 +1,6 @@
+import tailwindcss from '@tailwindcss/postcss'
+import autoprefixer from 'autoprefixer'
+
+export default {
+  plugins: [tailwindcss(), autoprefixer()],
+}