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/controllers/orders_controller.rb

@@ -270,6 +270,19 @@ class OrdersController < ApplicationController
       }
     end
 
+    # Add service fee as a separate line item
+    line_items << {
+      price_data: {
+        currency: "eur",
+        product_data: {
+          name: "Frais de service",
+          description: "Frais de traitement de la commande"
+        },
+        unit_amount: 100 # 1€ in cents
+      },
+      quantity: 1
+    }
+
     Stripe::Checkout::Session.create(
       payment_method_types: [ "card" ],
       line_items: line_items,