feat(billing): add missing payment methods and configurations

- Added migration to include global payment method configurations for Stripe and PayPal (both disabled).
- Ensured existing payment methods like bank transfer and manual payment are correctly configured.
- Added database constraints and indexes for improved data integrity in billing models.
- Introduced foreign key relationship between CreditTransaction and Payment models.
- Added webhook configuration fields to PaymentMethodConfig for future payment gateway integrations.
- Updated SignUpFormUnified component to handle payment method selection based on user country and plan.
- Implemented PaymentHistory component to display user's payment history with status indicators.

backend/igny8_core/auth/serializers.py

@@ -235,6 +235,9 @@ class SiteUserAccessSerializer(serializers.ModelSerializer):
         read_only_fields = ['granted_at']
 
 
+from igny8_core.business.billing.models import PAYMENT_METHOD_CHOICES
+
+
 class UserSerializer(serializers.ModelSerializer):
     account = AccountSerializer(read_only=True)
     accessible_sites = serializers.SerializerMethodField()
@@ -267,7 +270,7 @@ class RegisterSerializer(serializers.Serializer):
     )
     plan_slug = serializers.CharField(max_length=50, required=False)
     payment_method = serializers.ChoiceField(
-        choices=['stripe', 'paypal', 'bank_transfer', 'local_wallet'],
+        choices=[choice[0] for choice in PAYMENT_METHOD_CHOICES],
         default='bank_transfer',
         required=False
     )
@@ -291,6 +294,21 @@ class RegisterSerializer(serializers.Serializer):
         if 'plan_id' in attrs and attrs.get('plan_id') == '':
             attrs['plan_id'] = None
         
+        # Validate billing fields for paid plans
+        plan_slug = attrs.get('plan_slug')
+        paid_plans = ['starter', 'growth', 'scale']
+        if plan_slug and plan_slug in paid_plans:
+            # Require billing_country for paid plans
+            if not attrs.get('billing_country'):
+                raise serializers.ValidationError({
+                    "billing_country": "Billing country is required for paid plans."
+                })
+            # Require payment_method for paid plans
+            if not attrs.get('payment_method'):
+                raise serializers.ValidationError({
+                    "payment_method": "Payment method is required for paid plans."
+                })
+        
         return attrs
     
     def create(self, validated_data):