feat: add customer cart with expiry, shipping addresses with USPS validation, and multi-item PayPal checkout

frontend/src/main.tsx

@@ -9,7 +9,9 @@ import Login from './customer/Login';
 import Register from './customer/Register';
 import Account from './customer/Account';
 import PrivacyPolicy from './customer/PrivacyPolicy';
+import Cart from './cart/Cart';
 import { CustomerAuthProvider } from './customer/CustomerAuthContext';
+import { CartProvider } from './cart/CartContext';
 import { ThemeModeProvider, useThemeMode } from './theme/ThemeContext';
 import './styles.css';
 
@@ -29,6 +31,7 @@ function Root() {
           <Route path="/login" element={<Login />} />
           <Route path="/register" element={<Register />} />
           <Route path="/account" element={<Account />} />
+          <Route path="/cart" element={<Cart />} />
           <Route path="/privacy" element={<PrivacyPolicy />} />
         </Routes>
       </BrowserRouter>
@@ -40,7 +43,9 @@ ReactDOM.createRoot(document.getElementById('root')!).render(
   <React.StrictMode>
     <ThemeModeProvider>
       <CustomerAuthProvider>
-        <Root />
+        <CartProvider>
+          <Root />
+        </CartProvider>
       </CustomerAuthProvider>
     </ThemeModeProvider>
   </React.StrictMode>