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/payout.rb

@@ -12,18 +12,44 @@ class Payout < ApplicationRecord
   }, default: :pending
 
   # === Validations ===
-  validates :amount_cents, presence: true, numericality: { greater_than_or_equal_to: 0 }
+  validates :amount_cents, presence: true, numericality: { greater_than: 0 }
   validates :fee_cents, presence: true, numericality: { greater_than_or_equal_to: 0 }
   validates :status, presence: true
   validates :total_orders_count, presence: true, numericality: { greater_than_or_equal_to: 0 }
   validates :refunded_orders_count, presence: true, numericality: { greater_than_or_equal_to: 0 }
   validates :stripe_payout_id, allow_blank: true, uniqueness: true
+  validate :unique_pending_event_id, if: :pending?
+
+  validate :net_earnings_greater_than_zero, if: :pending?
+
+  def net_earnings_greater_than_zero
+    if event.net_earnings_cents <= 0
+      errors.add(:base, "net earnings must be greater than 0")
+    end
+  end
+
+  validate :net_earnings_greater_than_zero, if: :pending?
+
+  def net_earnings_greater_than_zero
+    if event.net_earnings_cents <= 0
+      errors.add(:base, "net earnings must be greater than 0")
+    end
+  end
+
+  def unique_pending_event_id
+    if Payout.pending.where(event_id: event_id).where.not(id: id).exists?
+      errors.add(:base, "only one pending payout allowed per event")
+    end
+  end
 
   # === Scopes ===
   scope :completed, -> { where(status: :completed) }
   scope :pending, -> { where(status: :pending) }
   scope :processing, -> { where(status: :processing) }
 
+  # === Callbacks ===
+  after_create :calculate_refunded_orders_count
+
   # === Instance Methods ===
 
   # Amount in euros (formatted)
@@ -56,4 +82,14 @@ class Payout < ApplicationRecord
     service = PayoutService.new(self)
     service.process!
   end
-end
+  public
+
+  # === Instance Methods ===
+
+  def calculate_refunded_orders_count
+    refunded_order_ids = event.tickets.where(status: "refunded").select(:order_id).distinct.pluck(:order_id)
+    paid_statuses = %w[paid completed]
+    count = event.orders.where(status: paid_statuses).where(id: refunded_order_ids).count
+    update_column(:refunded_orders_count, count)
+  end
+end