feat(payment): implement database-driven payment provider system with encrypted configuration support

- Add PaymentProviderSeeder with initial provider data (Stripe, Lemon Squeezy, Polar, OxaPay, Crypto, Activation Key)
  - Create migration to disable JSON constraints and change configuration column from JSON to TEXT
  - Update PaymentProvider model cast from 'array' to 'encrypted:array' for secure configuration storage

app/Models/PaymentProvider.php

@@ -24,7 +24,7 @@ class PaymentProvider extends Model
 
     protected $casts = [
         'is_active' => 'boolean',
-        'configuration' => 'array',
+        'configuration' => 'encrypted:array',
         'supports_recurring' => 'boolean',
         'supports_one_time' => 'boolean',
         'supported_currencies' => 'array',