feat: enhance Letzshop order import with EAN matching and stats

- Add historical order import with pagination support
- Add customer_locale, shipping_country_iso, billing_country_iso columns
- Add gtin/gtin_type columns to Product table for EAN matching
- Fix order stats to count all orders server-side (not just visible page)
- Add GraphQL introspection script with tracking workaround tests
- Enrich inventory units with EAN, MPN, SKU, product name
- Add LetzshopOrderStats schema for proper status counts

Migrations:
- a9a86cef6cca: Add locale and country fields to letzshop_orders
- cb88bc9b5f86: Add gtin columns to products table

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/integration/api/v1/admin/test_letzshop.py

@@ -287,9 +287,9 @@ class TestAdminLetzshopOrdersAPI:
                                 "id": "gid://letzshop/Order/111",
                                 "number": "LS-ADMIN-001",
                                 "email": "sync@example.com",
-                                "totalPrice": {"amount": "200.00", "currency": "EUR"},
+                                "total": "200.00",
                             },
-                            "inventoryUnits": {"nodes": []},
+                            "inventoryUnits": [],
                         }
                     ]
                 }

tests/integration/api/v1/vendor/test_letzshop.py

@@ -344,13 +344,11 @@ class TestVendorLetzshopOrdersAPI:
                                 "id": "gid://letzshop/Order/456",
                                 "number": "LS-2025-001",
                                 "email": "customer@example.com",
-                                "totalPrice": {"amount": "99.99", "currency": "EUR"},
-                            },
-                            "inventoryUnits": {
-                                "nodes": [
-                                    {"id": "unit_1", "state": "unconfirmed"},
-                                ]
+                                "total": "99.99",
                             },
+                            "inventoryUnits": [
+                                {"id": "unit_1", "state": "unconfirmed"},
+                            ],
                         }
                     ]
                 }