Add read-only admin functionality and enhance billing models in admin interface

backend/igny8_core/modules/billing/admin.py

@@ -4,7 +4,13 @@ Billing Module Admin
 from django.contrib import admin
 from django.utils.html import format_html
 from igny8_core.admin.base import AccountAdminMixin
-from igny8_core.business.billing.models import CreditCostConfig
+from igny8_core.business.billing.models import (
+    CreditCostConfig,
+    Invoice,
+    Payment,
+    CreditPackage,
+    PaymentMethodConfig,
+)
 from .models import CreditTransaction, CreditUsageLog, AccountPaymentMethod
 
 
@@ -44,6 +50,56 @@ class CreditUsageLogAdmin(AccountAdminMixin, admin.ModelAdmin):
     get_account_display.short_description = 'Account'
 
 
+@admin.register(Invoice)
+class InvoiceAdmin(AccountAdminMixin, admin.ModelAdmin):
+    list_display = [
+        'invoice_number',
+        'account',
+        'status',
+        'total',
+        'currency',
+        'invoice_date',
+        'due_date',
+        'subscription',
+    ]
+    list_filter = ['status', 'currency', 'invoice_date', 'account']
+    search_fields = ['invoice_number', 'account__name', 'subscription__id']
+    readonly_fields = ['created_at', 'updated_at']
+
+
+@admin.register(Payment)
+class PaymentAdmin(AccountAdminMixin, admin.ModelAdmin):
+    list_display = [
+        'id',
+        'invoice',
+        'account',
+        'payment_method',
+        'status',
+        'amount',
+        'currency',
+        'processed_at',
+    ]
+    list_filter = ['status', 'payment_method', 'currency', 'created_at']
+    search_fields = ['invoice__invoice_number', 'account__name', 'stripe_payment_intent_id', 'paypal_order_id']
+    readonly_fields = ['created_at', 'updated_at']
+
+
+@admin.register(CreditPackage)
+class CreditPackageAdmin(admin.ModelAdmin):
+    list_display = ['name', 'slug', 'credits', 'price', 'discount_percentage', 'is_active', 'is_featured', 'sort_order']
+    list_filter = ['is_active', 'is_featured']
+    search_fields = ['name', 'slug']
+    readonly_fields = ['created_at', 'updated_at']
+
+
+@admin.register(PaymentMethodConfig)
+class PaymentMethodConfigAdmin(admin.ModelAdmin):
+    list_display = ['country_code', 'payment_method', 'is_enabled', 'display_name', 'sort_order']
+    list_filter = ['payment_method', 'is_enabled', 'country_code']
+    search_fields = ['country_code', 'display_name', 'payment_method']
+    readonly_fields = ['created_at', 'updated_at']
+
+
 @admin.register(AccountPaymentMethod)
 class AccountPaymentMethodAdmin(AccountAdminMixin, admin.ModelAdmin):
     list_display = [