refactor(pricing): implement hybrid fee model (€0.50 + 1.5%) deducted from promoter payout

- Remove 1€ fixed fee from orders and Stripe invoices
- Add platform_fee_cents, promoter_payout_cents methods to Order model
- Update views to show clean ticket totals without added fees
- Update tests for new fee calculation logic
- Update pricing docs with implemented model

app/models/order.rb

@@ -88,11 +88,32 @@ class Order < ApplicationRecord
     end
   end
 
-  # Calculate total from tickets plus 1€ service fee
+  # Calculate total from ticket prices only (platform fee deducted from promoter payout)
   def calculate_total!
     ticket_total = tickets.sum(:price_cents)
-    fee_cents = 100 # 1€ in cents
-    update!(total_amount_cents: ticket_total + fee_cents)
+    update!(total_amount_cents: ticket_total)
+  end
+
+  # Platform fee: €0.50 fixed + 1.5% of ticket price, per ticket
+  def platform_fee_cents
+    tickets.sum do |ticket|
+      fixed_fee = 50 # €0.50 in cents
+      percentage_fee = (ticket.price_cents * 0.015).to_i
+      fixed_fee + percentage_fee
+    end
+  end
+
+  # Promoter payout amount after platform fee deduction
+  def promoter_payout_cents
+    total_amount_cents - platform_fee_cents
+  end
+
+  def platform_fee_euros
+    platform_fee_cents / 100.0
+  end
+
+  def promoter_payout_euros
+    promoter_payout_cents / 100.0
   end
 
   # Create Stripe invoice for accounting records