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

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_09_16_221454) do
+ActiveRecord::Schema[8.0].define(version: 2025_09_16_230003) do
   create_table "earnings", charset: "utf8mb4", collation: "utf8mb4_uca1400_ai_ci", force: :cascade do |t|
     t.integer "amount_cents"
     t.integer "fee_cents"
@@ -24,6 +24,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_16_221454) do
     t.datetime "updated_at", null: false
     t.index ["event_id"], name: "index_earnings_on_event_id"
     t.index ["order_id"], name: "index_earnings_on_order_id"
+    t.index ["status"], name: "index_earnings_on_status"
     t.index ["user_id"], name: "index_earnings_on_user_id"
   end
 
@@ -81,6 +82,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_16_221454) do
     t.bigint "event_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["event_id", "status"], name: "index_payouts_on_event_id_and_status"
     t.index ["event_id"], name: "index_payouts_on_event_id"
     t.index ["status"], name: "index_payouts_on_status"
     t.index ["stripe_payout_id"], name: "index_payouts_on_stripe_payout_id", unique: true
@@ -116,6 +118,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_09_16_221454) do
     t.datetime "updated_at", null: false
     t.index ["order_id"], name: "index_tickets_on_order_id"
     t.index ["qr_code"], name: "index_tickets_on_qr_code", unique: true
+    t.index ["status", "order_id"], name: "index_tickets_on_status_and_order_id"
     t.index ["ticket_type_id"], name: "index_tickets_on_ticket_type_id"
   end