Fix Decimal+float TypeError in cart total calculation

Product prices are float from DB but calendar/ticket totals are Decimal,
causing TypeError when summed in cart_context. Wrap prices in Decimal().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bp/cart/services/total.py

@@ -1,6 +1,12 @@
+from decimal import Decimal
+
+
 def total(cart):
     return sum(
-        (item.product.special_price or item.product.regular_price) * item.quantity
+        (
+            Decimal(str(item.product.special_price or item.product.regular_price))
+            * item.quantity
+        )
         for item in cart
         if (item.product.special_price or item.product.regular_price) is not None
     )