feat: implement comprehensive multi-provider payment processing system

- Add unified payment provider architecture with contract-based design
  - Implement 6 payment providers: Stripe, Lemon Squeezy, Polar, Oxapay, Crypto, Activation Keys
  - Create subscription management with lifecycle handling (create, cancel, pause, resume, update)
  - Add coupon system with usage tracking and trial extensions
  - Build Filament admin resources for payment providers, subscriptions, coupons, and trials
  - Implement payment orchestration service with provider registry and configuration management
  - Add comprehensive payment logging and webhook handling for all providers
  - Create customer analytics dashboard with revenue, churn, and lifetime value metrics
  - Add subscription migration service for provider switching
  - Include extensive test coverage for all payment functionality

.env.example

@@ -75,9 +75,6 @@ REMOTE_DB_PASSWORD=
 NOTIFY_TG_BOT_TOKEN=
 NOTIFY_TG_CHAT_ID=
 
-OXAPAY_MERCHANT_API_KEY=
-OXAPAY_PAYOUT_API_KEY=
-
 FORCE_DB_MAIL=false
 AUTO_FETCH_MAIL=false
 FETCH_FETCH_FOR_DB=true
@@ -88,8 +85,50 @@ MOVE_OR_DELETE=delete
 STRIPE_KEY=
 STRIPE_SECRET=
 STRIPE_WEBHOOK_SECRET=
+STRIPE_PUBLISHABLE_KEY=
+STRIPE_SUCCESS_URL=/payment/success
+STRIPE_CANCEL_URL=/payment/cancel
 CASHIER_LOGGER=stack
 
+# Lemon Squeezy Payment Provider
+LEMON_SQUEEZY_API_KEY=
+LEMON_SQUEEZY_STORE_ID=
+LEMON_SQUEEZY_WEBHOOK_SECRET=
+LEMON_SQUEEZY_SUCCESS_URL=/payment/success
+LEMON_SQUEEZY_CANCEL_URL=/payment/cancel
+
+# Polar.sh Payment Provider
+POLAR_API_KEY=
+POLAR_WEBHOOK_SECRET=
+POLAR_ACCESS_TOKEN=
+POLAR_SUCCESS_URL=/payment/success
+POLAR_CANCEL_URL=/payment/cancel
+
+# OxaPay Payment Provider
+OXAPAY_MERCHANT_API_KEY=
+OXAPAY_PAYOUT_API_KEY=
+OXAPAY_WEBHOOK_URL=
+OXAPAY_SUCCESS_URL=/payment/success
+OXAPAY_CANCEL_URL=/payment/cancel
+OXAPAY_SANDBOX=false
+
+# Crypto Payment Provider
+CRYPTO_PAYMENTS_ENABLED=false
+CRYPTO_WEBHOOK_SECRET=
+CRYPTO_CONFIRMATION_TIMEOUT=30
+CRYPTO_EXCHANGE_RATE_PROVIDER=coingecko
+COINGECKO_API_KEY=
+BLOCKCHAIR_API_KEY=
+CRYPTO_SUCCESS_URL=/payment/success
+CRYPTO_CANCEL_URL=/payment/cancel
+
+# Activation Key Provider
+ACTIVATION_KEY_PREFIX=AK-
+ACTIVATION_KEY_LENGTH=32
+ACTIVATION_KEY_EXPIRATION_DAYS=
+ACTIVATION_KEY_REQUIRE_EMAIL=true
+ACTIVATION_KEY_MAX_PER_USER=5
+
 FILAMENT_LOG_VIEWER_DRIVER=raw
 
 #IMAP_HOST=