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/controllers/admin/payouts_controller_test.rb

@@ -0,0 +1,48 @@
+require "test_helper"
+
+class Admin::PayoutsControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @admin_user = User.create!(email: "admin@example.com", password: "password123", password_confirmation: "password123", is_professionnal: true)
+    @admin_user.add_role :admin  # Assume role system
+    @payout = payouts(:one)
+  end
+
+  test "process payout success for pending payout" do
+    sign_in @admin_user
+    @payout.update(status: :pending)
+
+    # Mock service
+    PayoutService.any_instance.expects(:process!).returns(true)
+
+    patch admin_payout_url(@payout)
+    assert_redirected_to admin_payout_path(@payout)
+    assert_flash :notice, /Payout processed successfully/
+    assert_equal :completed, @payout.reload.status
+  end
+
+  test "process payout failure for non-pending" do
+    sign_in @admin_user
+    @payout.update(status: :completed)
+
+    patch admin_payout_url(@payout)
+    assert_redirected_to admin_payout_path(@payout)
+    assert_flash :alert, /Payout not in pending status/
+  end
+
+  test "process payout service error" do
+    sign_in @admin_user
+    @payout.update(status: :pending)
+
+    PayoutService.any_instance.expects(:process!).raises(StandardError.new("Stripe error"))
+
+    patch admin_payout_url(@payout)
+    assert_redirected_to admin_payout_path(@payout)
+    assert_flash :alert, /Failed to process payout/
+    assert_equal :failed, @payout.reload.status
+  end
+
+  test "requires admin authentication" do
+    patch admin_payout_url(@payout)
+    assert_redirected_to new_user_session_path
+  end
+end