feat(payouts): implement promoter earnings viewing, request flow, and admin Stripe processing with webhooks

Add model methods for accurate net calculations (€0.50 + 1.5% fees), eligibility, refund handling
Update promoter/payouts controller for index (pending events), create (eligibility checks)
Integrate admin processing via Stripe::Transfer, webhook for status sync
Enhance views: index pending cards, events/show preview/form
Add comprehensive tests (models, controllers, service, integration); run migrations

test/fixtures/orders.yml

@@ -1,3 +1,13 @@
+one:
+  user: one
+  event: concert_event
+  status: paid
+  total_amount_cents: 2500
+  payment_attempts: 1
+  expires_at: <%= 1.hour.from_now %>
+  created_at: <%= 1.hour.ago %>
+  updated_at: <%= 1.hour.ago %>
+
 paid_order:
   user: one
   event: concert_event
@@ -26,4 +36,14 @@ expired_order:
   payment_attempts: 1
   expires_at: <%= 1.hour.ago %>
   created_at: <%= 2.hours.ago %>
-  updated_at: <%= 1.hour.ago %>
+  updated_at: <%= 1.hour.ago %>
+
+two:
+  user: two
+  event: winter_gala
+  status: expired
+  total_amount_cents: 5000
+  payment_attempts: 2
+  expires_at: <%= 2.hours.ago %>
+  created_at: <%= 3.hours.ago %>
+  updated_at: <%= 2.hours.ago %>