Add 1€ service fee to all order-related pages and Stripe integration

- Added 1€ service fee to order total calculation in Order model
- Updated checkout page to display fee breakdown (subtotal + 1€ fee = total)
- Updated payment success page to show fee breakdown
- Updated order show page to display fee breakdown
- Updated payment cancel page to show fee breakdown
- Modified Stripe session creation to include service fee as separate line item
- Updated order model tests to account for the 1€ service fee
- Enhanced overall pricing transparency for users

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

app/models/order.rb

@@ -88,9 +88,11 @@ class Order < ApplicationRecord
     end
   end
 
-  # Calculate total from tickets
+  # Calculate total from tickets plus 1€ service fee
   def calculate_total!
-    update!(total_amount_cents: tickets.sum(:price_cents))
+    ticket_total = tickets.sum(:price_cents)
+    fee_cents = 100 # 1€ in cents
+    update!(total_amount_cents: ticket_total + fee_cents)
   end
 
   # Create Stripe invoice for accounting records