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

items/tests.py

@@ -4,6 +4,7 @@ from django.core.exceptions import ValidationError
 
 from favorites.models import Favorite
 from items.models import Category, Item, ItemImage, Subcategory
+from orders.models import Cart, CartItem
 
 
 @override_settings(MEDIA_URL="/media/")
@@ -215,6 +216,44 @@ class CatalogViewTests(TestCase):
 
         self.assertEqual(response.status_code, 404)
 
+    def test_detail_page_shows_cart_link_for_item_already_in_cart(self):
+        user = get_user_model().objects.create_user(
+            username="cart-user",
+            email="cart-user@example.com",
+            password="StrongPassword123",
+            is_active=True,
+        )
+        cart = Cart.objects.create(user=user)
+        CartItem.objects.create(cart=cart, item=self.sink, quantity=1)
+        self.client.force_login(user)
+
+        response = self.client.get("/catalog/plumbing/kitchen-sink/")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, 'href="/orders/cart/"', html=False)
+        self.assertContains(response, "Перейти в корзину")
+
+    def test_detail_page_guest_cart_cta_redirects_to_login(self):
+        response = self.client.get("/catalog/plumbing/kitchen-sink/")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(
+            response,
+            'href="/users/login/?next=/catalog/plumbing/kitchen-sink/"',
+            html=False,
+        )
+        self.assertNotContains(response, "data-guest-cart-detail-button", html=False)
+
+    def test_header_cart_link_redirects_guest_to_login(self):
+        response = self.client.get("/catalog/")
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(
+            response,
+            'href="/users/login/?next=/orders/cart/"',
+            html=False,
+        )
+
     def test_detail_page_wrong_category_returns_404(self):
         response = self.client.get("/catalog/decor/kitchen-sink/")
 

items/views.py

@@ -5,6 +5,7 @@ from django.shortcuts import render
 
 from favorites.services import get_user_favorite_item_ids
 from items.models import Category, Item, Subcategory
+from orders.services import get_user_cart_item_ids
 
 
 @dataclass
@@ -78,5 +79,6 @@ def detail(request: HttpRequest, category: str, slug: str) -> HttpResponse:
         'item': item,
         'images': images,
         'primary_image': images[0] if images else None,
+        'cart_item_ids': get_user_cart_item_ids(request.user),
         'favorite_item_ids': get_user_favorite_item_ids(request.user),
     })