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/services/payout_service_test.rb

@@ -0,0 +1,72 @@
+
+require "test_helper"
+require "stripe"
+
+class PayoutServiceTest < ActiveSupport::TestCase
+  setup do
+    @user = users(:one)
+    @event = events(:concert_event)
+    @payout = Payout.create!(user: @user, event: @event, amount_cents: 9000, fee_cents: 1000)
+    Stripe.api_key = "test_key"
+  end
+
+  test "process! success creates transfer and updates status" do
+    # Mock Stripe Transfer
+    Stripe::Transfer.expects(:create).with(
+      amount: 90,  # cents to euros
+      currency: "eur",
+      destination: @user.stripe_connected_account_id,
+      description: "Payout for event #{@event.name}"
+    ).returns(stub(id: "tr_123", status: "succeeded"))
+
+    @payout.update(status: :pending)
+
+    service = PayoutService.new(@payout)
+    service.process!
+
+    @payout.reload
+    assert_equal :completed, @payout.status
+    assert_equal "tr_123", @payout.stripe_payout_id
+    assert @payout.earnings.update_all(status: :paid)  # assume update_earnings_status
+  end
+
+  test "process! failure with Stripe error sets status to failed" do
+    Stripe::Transfer.expects(:create).raises(Stripe::CardError.new("Insufficient funds"))
+
+    @payout.update(status: :pending)
+
+    service = PayoutService.new(@payout)
+    assert_raises Stripe::CardError do
+      service.process!
+    end
+
+    @payout.reload
+    assert_equal :failed, @payout.status
+    assert_not_nil @payout.error_message  # assume logged
+  end
+
+  test "process! idempotent for already completed" do
+    @payout.update(status: :completed, stripe_payout_id: "tr_456")
+
+    Stripe::Transfer.expects(:create).never
+
+    service = PayoutService.new(@payout)
+    service.process!
+
+    @payout.reload
+    assert_equal :completed, @payout.status
+  end
+
+  test "update_earnings_status marks earnings as paid" do
+    earning1 = Earning.create!(event: @event, user: @user, order: orders(:one), amount_cents: 4500, fee_cents: 500, status: :pending)
+    earning2 = Earning.create!(event: @event, user: @user, order: orders(:two), amount_cents: 4500, fee_cents: 500, status: :pending)
+    @payout.earnings << earning1
+    @payout.earnings << earning2
+
+    service = PayoutService.new(@payout)
+    service.update_earnings_status(:paid)
+
+    assert_equal :paid, earning1.reload.status
+    assert_equal :paid, earning2.reload.status
+  end
+end