feat: refine price formatting and enable dynamic color updates in cart

- Updated price slider and backend formatting to round values instead of showing decimals
- Enhanced product detail page with active color selection display and automatic cart updates
- Adjusted swatch behavior to dynamically update the selected color in the cart via AJAX
- Improved consistency in slider steps and price formatting throughout templates and views

items/views.py

@@ -8,6 +8,7 @@ from django.shortcuts import redirect, render
 
 from favorites.services import get_user_favorite_item_ids
 from items.models import Category, Color, Item, Subcategory
+from orders.models import CartItem
 from orders.services import get_user_cart_item_ids
 
 
@@ -90,7 +91,7 @@ def _resolve_catalog_scope(scope_value: str | None) -> tuple[str | None, str | N
 
 
 def _format_price_value(value: Decimal) -> str:
-    return format(value, "f")
+    return str(int(value))
 
 
 def index(request: HttpRequest, category: str | None = None) -> HttpResponse:
@@ -322,11 +323,20 @@ def detail(request: HttpRequest, category: str, slug: str) -> HttpResponse:
 
     images = list(item.images.all())
 
+    cart_color_id = None
+    if request.user.is_authenticated:
+        cart_item = CartItem.objects.filter(
+            cart__user=request.user, item=item
+        ).select_related('selected_color').first()
+        if cart_item and cart_item.selected_color_id:
+            cart_color_id = cart_item.selected_color_id
+
     return render(request, 'catalog/detail.html', {
         'categories': Category.objects.order_by('name'),
         'item': item,
         'images': images,
         'primary_image': images[0] if images else None,
         'cart_item_ids': get_user_cart_item_ids(request.user),
+        'cart_color_id': cart_color_id,
         'favorite_item_ids': get_user_favorite_item_ids(request.user),
     })