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

app/Contracts/Payments/PaymentProviderContract.php

@@ -0,0 +1,171 @@
+<?php
+
+namespace App\Contracts\Payments;
+
+use App\Models\Plan;
+use App\Models\Subscription;
+use App\Models\User;
+use Illuminate\Http\Request;
+
+interface PaymentProviderContract
+{
+    /**
+     * Get the provider name/identifier
+     */
+    public function getName(): string;
+
+    /**
+     * Check if provider is properly configured and active
+     */
+    public function isActive(): bool;
+
+    /**
+     * Create a new subscription for a user
+     */
+    public function createSubscription(User $user, Plan $plan, array $options = []): array;
+
+    /**
+     * Cancel an existing subscription
+     */
+    public function cancelSubscription(Subscription $subscription, string $reason = ''): bool;
+
+    /**
+     * Update an existing subscription (e.g., change plan)
+     */
+    public function updateSubscription(Subscription $subscription, Plan $newPlan): array;
+
+    /**
+     * Pause a subscription
+     */
+    public function pauseSubscription(Subscription $subscription): bool;
+
+    /**
+     * Resume a paused subscription
+     */
+    public function resumeSubscription(Subscription $subscription): bool;
+
+    /**
+     * Get subscription details from provider
+     */
+    public function getSubscriptionDetails(string $providerSubscriptionId): array;
+
+    /**
+     * Create a checkout session for one-time payment
+     */
+    public function createCheckoutSession(User $user, Plan $plan, array $options = []): array;
+
+    /**
+     * Create a customer portal session
+     */
+    public function createCustomerPortalSession(User $user): array;
+
+    /**
+     * Process webhook events from provider
+     */
+    public function processWebhook(Request $request): array;
+
+    /**
+     * Validate webhook signature
+     */
+    public function validateWebhook(Request $request): bool;
+
+    /**
+     * Get provider-specific configuration
+     */
+    public function getConfiguration(): array;
+
+    /**
+     * Sync subscription status from provider
+     */
+    public function syncSubscriptionStatus(Subscription $subscription): array;
+
+    /**
+     * Get payment method details
+     */
+    public function getPaymentMethodDetails(string $paymentMethodId): array;
+
+    /**
+     * Handle refund
+     */
+    public function processRefund(string $paymentIntentId, float $amount, string $reason = ''): array;
+
+    /**
+     * Get transaction history
+     */
+    public function getTransactionHistory(User $user, array $filters = []): array;
+
+    /**
+     * Calculate fees for a transaction
+     */
+    public function calculateFees(float $amount): array;
+
+    /**
+     * Get supported currencies
+     */
+    public function getSupportedCurrencies(): array;
+
+    /**
+     * Check if provider supports recurring subscriptions
+     */
+    public function supportsRecurring(): bool;
+
+    /**
+     * Check if provider supports one-time payments
+     */
+    public function supportsOneTime(): bool;
+
+    /**
+     * Get provider-specific metadata for subscription
+     */
+    public function getSubscriptionMetadata(Subscription $subscription): array;
+
+    /**
+     * Update provider-specific metadata
+     */
+    public function updateSubscriptionMetadata(Subscription $subscription, array $metadata): bool;
+
+    /**
+     * Handle subscription trial
+     */
+    public function startTrial(Subscription $subscription, int $trialDays): bool;
+
+    /**
+     * Apply coupon/discount
+     */
+    public function applyCoupon(Subscription $subscription, string $couponCode): array;
+
+    /**
+     * Remove applied coupon
+     */
+    public function removeCoupon(Subscription $subscription): bool;
+
+    /**
+     * Get upcoming invoice details
+     */
+    public function getUpcomingInvoice(Subscription $subscription): array;
+
+    /**
+     * Handle failed payment retry
+     */
+    public function retryFailedPayment(Subscription $subscription): array;
+
+    /**
+     * Check if subscription can be modified
+     */
+    public function canModifySubscription(Subscription $subscription): bool;
+
+    /**
+     * Get subscription cancellation terms
+     */
+    public function getCancellationTerms(Subscription $subscription): array;
+
+    /**
+     * Export subscription data for migration
+     */
+    public function exportSubscriptionData(Subscription $subscription): array;
+
+    /**
+     * Import subscription data from another provider
+     */
+    public function importSubscriptionData(User $user, array $subscriptionData): array;
+}