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

database/factories/SubscriptionChangeFactory.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Database\Factories;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends \Illuminate\Database\Eloquent\Factories\Factory<\App\Models\SubscriptionChange>
+ */
+class SubscriptionChangeFactory extends Factory
+{
+    /**
+     * Define the model's default state.
+     *
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        $changeType = fake()->randomElement([
+            'plan_change', 'cancellation', 'pause', 'resume', 'migration', 'provider_change',
+        ]);
+
+        return [
+            'subscription_id' => \App\Models\Subscription::factory(),
+            'user_id' => \App\Models\User::factory(),
+            'change_type' => $changeType,
+            'change_description' => fake()->sentence(),
+            'old_values' => fake()->optional(0.7)->randomElement([
+                ['plan_id' => fake()->numberBetween(1, 5), 'price' => fake()->randomFloat(2, 10, 100)],
+                ['status' => 'active', 'provider' => 'stripe'],
+            ]),
+            'new_values' => fake()->optional(0.7)->randomElement([
+                ['plan_id' => fake()->numberBetween(1, 5), 'price' => fake()->randomFloat(2, 10, 100)],
+                ['status' => 'cancelled', 'provider' => 'lemon_squeezy'],
+            ]),
+            'reason' => fake()->optional(0.6)->randomElement([
+                'Customer request',
+                'Payment failure',
+                'Plan upgrade',
+                'Service downgrade',
+                'Technical migration',
+            ]),
+            'effective_at' => fake()->dateTimeBetween('-1 month', 'now'),
+            'processed_at' => fake()->optional(0.8)->dateTimeBetween('-1 month', 'now'),
+            'is_processed' => fake()->boolean(80),
+            'metadata' => fake()->optional(0.2)->randomElements([
+                'processed_by' => fake()->name(),
+                'system_generated' => fake()->boolean(),
+                'batch_id' => fake()->uuid(),
+            ]),
+        ];
+    }
+}