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>

models/schema/letzshop.py

@@ -130,6 +130,15 @@ class LetzshopOrderDetailResponse(LetzshopOrderResponse):
     raw_order_data: dict[str, Any] | None = None
 
 
+class LetzshopOrderStats(BaseModel):
+    """Schema for order statistics by status."""
+
+    pending: int = 0
+    confirmed: int = 0
+    rejected: int = 0
+    shipped: int = 0
+
+
 class LetzshopOrderListResponse(BaseModel):
     """Schema for paginated Letzshop order list."""
 
@@ -137,6 +146,7 @@ class LetzshopOrderListResponse(BaseModel):
     total: int
     skip: int
     limit: int
+    stats: LetzshopOrderStats | None = None  # Order counts by sync_status
 
 
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