feat: redesign Letzshop products tab with product listing view

Products Tab Changes:
- Converted to product listing page similar to /admin/marketplace-products
- Added Import/Export buttons in header
- Added product stats cards (total, active, inactive, last sync)
- Added search and filter functionality
- Added product table with pagination
- Import modal for single URL or all languages

Settings Tab Changes:
- Moved batch size setting from products tab
- Moved include inactive checkbox from products tab
- Added export behavior info box

Export Changes:
- New POST endpoint exports all languages (FR, DE, EN)
- CSV files written to exports/letzshop/{vendor_code}/ for scheduler pickup
- Letzshop scheduler can fetch files from this location

API Changes:
- Added vendor_id filter to /admin/vendor-products/stats endpoint
- Added POST /admin/vendors/{id}/export/letzshop for folder export

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

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

app/services/vendor_product_service.py

@@ -75,12 +75,24 @@ class VendorProductService:
 
         return result, total
 
-    def get_product_stats(self, db: Session) -> dict:
-        """Get vendor product statistics for admin dashboard."""
-        total = db.query(func.count(Product.id)).scalar() or 0
+    def get_product_stats(self, db: Session, vendor_id: int | None = None) -> dict:
+        """Get vendor product statistics for admin dashboard.
+
+        Args:
+            db: Database session
+            vendor_id: Optional vendor ID to filter stats
+
+        Returns:
+            Dict with product counts (total, active, inactive, etc.)
+        """
+        # Base query filter
+        base_filter = Product.vendor_id == vendor_id if vendor_id else True
+
+        total = db.query(func.count(Product.id)).filter(base_filter).scalar() or 0
 
         active = (
             db.query(func.count(Product.id))
+            .filter(base_filter)
             .filter(Product.is_active == True)  # noqa: E712
             .scalar()
             or 0
@@ -89,6 +101,7 @@ class VendorProductService:
 
         featured = (
             db.query(func.count(Product.id))
+            .filter(base_filter)
             .filter(Product.is_featured == True)  # noqa: E712
             .scalar()
             or 0
@@ -97,6 +110,7 @@ class VendorProductService:
         # Digital/physical counts
         digital = (
             db.query(func.count(Product.id))
+            .filter(base_filter)
             .join(Product.marketplace_product)
             .filter(Product.marketplace_product.has(is_digital=True))
             .scalar()
@@ -104,17 +118,19 @@ class VendorProductService:
         )
         physical = total - digital
 
-        # Count by vendor
-        vendor_counts = (
-            db.query(
-                Vendor.name,
-                func.count(Product.id),
+        # Count by vendor (only when not filtered by vendor_id)
+        by_vendor = {}
+        if not vendor_id:
+            vendor_counts = (
+                db.query(
+                    Vendor.name,
+                    func.count(Product.id),
+                )
+                .join(Vendor, Product.vendor_id == Vendor.id)
+                .group_by(Vendor.name)
+                .all()
             )
-            .join(Vendor, Product.vendor_id == Vendor.id)
-            .group_by(Vendor.name)
-            .all()
-        )
-        by_vendor = {name or "unknown": count for name, count in vendor_counts}
+            by_vendor = {name or "unknown": count for name, count in vendor_counts}
 
         return {
             "total": total,