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/controllers/admin/payouts_controller.rb

@@ -3,19 +3,25 @@ class Admin::PayoutsController < ApplicationController
   before_action :ensure_admin!
 
   def index
-    @payouts = Payout.includes(:event, :user)
-                     .order(created_at: :desc)
-                     .page(params[:page])
+    @payouts = Payout.pending.includes(:user, :event).order(created_at: :asc).page(params[:page])
   end
 
-  def create
+  def show
     @payout = Payout.find(params[:id])
-    
-    begin
-      @payout.process_payout!
-      redirect_to admin_payouts_path, notice: "Payout processed successfully."
-    rescue => e
-      redirect_to admin_payouts_path, alert: "Failed to process payout: #{e.message}"
+  end
+
+  def process
+    @payout = Payout.find(params[:id])
+
+    if @payout.pending? && @payout.can_process?
+      begin
+        PayoutService.new(@payout).process!
+        redirect_to admin_payouts_path, notice: "Payout processed successfully."
+      rescue => e
+        redirect_to admin_payouts_path, alert: "Failed to process payout: #{e.message}"
+      end
+    else
+      redirect_to admin_payouts_path, alert: "Cannot process this payout."
     end
   end
 
@@ -28,4 +34,4 @@ class Admin::PayoutsController < ApplicationController
       redirect_to dashboard_path, alert: "Access denied."
     end
   end
-end
+end