Migrate to global currency system in commerce app

Removed per-product currency in favor of a global site currency managed via SiteConfiguration. Updated models, views, templates, and Stripe integration to use the global currency. Added migration, management command for migration, and API endpoint for currency info. Improved permissions and filtering for orders, reviews, and carts. Expanded supported currencies in configuration.

backend/commerce/management/commands/migrate_to_global_currency.py

@@ -0,0 +1,74 @@
+"""
+Management command to migrate from per-product currency to global currency system.
+Usage: python manage.py migrate_to_global_currency
+"""
+from django.core.management.base import BaseCommand
+from commerce.models import Product, Order
+from configuration.models import SiteConfiguration
+
+
+class Command(BaseCommand):
+    help = 'Migrate from per-product currency to global currency system'
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            '--target-currency',
+            type=str,
+            default='EUR',
+            help='Target currency to migrate to (default: EUR)'
+        )
+        parser.add_argument(
+            '--dry-run',
+            action='store_true',
+            help='Show what would be changed without making changes'
+        )
+
+    def handle(self, *args, **options):
+        target_currency = options['target_currency']
+        dry_run = options['dry_run']
+        
+        self.stdout.write(
+            self.style.SUCCESS(f"Migrating to global currency: {target_currency}")
+        )
+        
+        # Check current state
+        config = SiteConfiguration.get_solo()
+        self.stdout.write(f"Current site currency: {config.currency}")
+        
+        if hasattr(Product.objects.first(), 'currency'):
+            # Products still have currency field
+            product_currencies = Product.objects.values_list('currency', flat=True).distinct()
+            self.stdout.write(f"Product currencies found: {list(product_currencies)}")
+            
+            if len(product_currencies) > 1:
+                self.stdout.write(
+                    self.style.WARNING(
+                        "Multiple currencies detected in products. "
+                        "Consider currency conversion before migration."
+                    )
+                )
+        
+        order_currencies = Order.objects.values_list('currency', flat=True).distinct()
+        order_currencies = [c for c in order_currencies if c]  # Remove empty strings
+        self.stdout.write(f"Order currencies found: {list(order_currencies)}")
+        
+        if not dry_run:
+            # Update site configuration
+            config.currency = target_currency
+            config.save()
+            self.stdout.write(
+                self.style.SUCCESS(f"Updated site currency to {target_currency}")
+            )
+            
+            # Update orders with empty currency
+            orders_updated = Order.objects.filter(currency='').update(currency=target_currency)
+            self.stdout.write(
+                self.style.SUCCESS(f"Updated {orders_updated} orders to use {target_currency}")
+            )
+            
+        else:
+            self.stdout.write(self.style.WARNING("DRY RUN - No changes made"))
+            
+        self.stdout.write(
+            self.style.SUCCESS("Migration completed successfully!")
+        )