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

app/models/earning.rb

@@ -1,4 +1,22 @@
 class Earning < ApplicationRecord
+  def self.create_from_order(order)
+    return unless order.paid? || order.completed?
+
+    gross_cents = order.tickets.active.sum(:price_cents)
+    fee_cents = order.tickets.active.sum do |ticket|
+      50 + (ticket.price_cents * 0.015).to_i
+    end
+    amount_cents = gross_cents - fee_cents
+
+    create!(
+      event: order.event,
+      user: order.event.user,
+      order: order,
+      amount_cents: amount_cents,
+      fee_cents: fee_cents,
+      status: :pending
+    )
+  end
   # === Relations ===
   belongs_to :event
   belongs_to :user
@@ -13,4 +31,24 @@ class Earning < ApplicationRecord
   validates :net_amount_cents, numericality: { greater_than_or_equal_to: 0, allow_nil: true }
   validates :status, presence: true
   validates :stripe_payout_id, allow_blank: true, uniqueness: true
+
+  # Recalculate earning based on active tickets in the order
+  def recalculate!
+    return unless order.present?
+
+    active_tickets = order.tickets.active
+    if active_tickets.empty?
+      update!(amount_cents: 0, fee_cents: 0)
+    else
+      gross_cents = active_tickets.sum(:price_cents)
+      fee_cents = active_tickets.sum do |ticket|
+        50 + (ticket.price_cents * 0.015).to_i
+      end
+      update!(amount_cents: gross_cents - fee_cents, fee_cents: fee_cents)
+    end
+  end
+
+  def recalculate_on_refund(order)
+    recalculate!
+  end
 end