feat: implement shopping cart feature with user authentication support

- Added `Cart` and `CartItem` models with migrations for managing user-specific carts and items
- Developed services for cart-related operations: adding, removing, and updating cart items
- Built specialized templates (`cart.html`) and styled them with new CSS assets (`cart.css`)
- Enabled real-time UI updates via AJAX in shopping cart interactions (`cart.js`)
- Modified header to dynamically display cart link with user authentication awareness
- Added Leaflet-based interactive map to the contacts page and integrated CSS/JS dependencies
- Expanded tests for cart functionality, item detail page cart integration, and contacts page maps

users/tests.py

@@ -6,7 +6,6 @@ from django.urls import reverse
 from django.utils.encoding import force_bytes
 from django.utils.http import urlsafe_base64_encode
 
-
 User = get_user_model()
 
 
@@ -17,6 +16,7 @@ class UserAuthFlowTests(TestCase):
 
         self.assertEqual(response.status_code, 200)
         self.assertTemplateUsed(response, "users/login.html")
+        self.assertNotContains(response, 'name="guest_cart_payload"', html=False)
 
     def test_registration_creates_inactive_user_and_sends_activation_email(self):
         response = self.client.post(
@@ -101,3 +101,9 @@ class UserAuthFlowTests(TestCase):
         self.assertRedirects(response, reverse("users:password_reset_done"))
         self.assertEqual(len(mail.outbox), 1)
         self.assertIn("/users/reset/", mail.outbox[0].body)
+
+    def test_registration_page_does_not_render_guest_cart_payload_field(self):
+        response = self.client.get(reverse("users:register"))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertNotContains(response, 'name="guest_cart_payload"', html=False)