feat: add item-level order confirmation/decline support

Per Letzshop API, each inventory unit must be confirmed/declined individually.
This enables partial confirmation (some items confirmed, others declined).

Admin API endpoints:
- POST /vendors/{id}/orders/{id}/confirm - confirm all items
- POST /vendors/{id}/orders/{id}/reject - decline all items
- POST /vendors/{id}/orders/{id}/items/{id}/confirm - confirm single item
- POST /vendors/{id}/orders/{id}/items/{id}/decline - decline single item

Order detail modal now shows:
- Product name, EAN, SKU, MPN, price per item
- Per-item state badge (unconfirmed/confirmed/declined)
- Per-item confirm/decline buttons for pending items
- Bulk confirm/decline all buttons

Order status logic:
- If all items declined -> order is "declined"
- If any item confirmed -> order is "confirmed"
- Partial confirmation supported

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

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

app/api/v1/admin/letzshop.py

@@ -22,10 +22,12 @@ from app.services.letzshop import (
     LetzshopClientError,
     LetzshopCredentialsService,
     LetzshopOrderService,
+    OrderNotFoundError,
     VendorNotFoundError,
 )
 from models.database.user import User
 from models.schema.letzshop import (
+    FulfillmentOperationResponse,
     LetzshopConnectionTestRequest,
     LetzshopConnectionTestResponse,
     LetzshopCredentialsCreate,
@@ -647,3 +649,246 @@ def get_import_summary(
         "success": True,
         "summary": summary,
     }
+
+
+# ============================================================================
+# Fulfillment Operations (Admin)
+# ============================================================================
+
+
+@router.post(
+    "/vendors/{vendor_id}/orders/{order_id}/confirm",
+    response_model=FulfillmentOperationResponse,
+)
+def confirm_order(
+    vendor_id: int = Path(..., description="Vendor ID"),
+    order_id: int = Path(..., description="Order ID"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Confirm all inventory units for a Letzshop order.
+
+    Sends confirmInventoryUnits mutation with isAvailable=true for all items.
+    """
+    order_service = get_order_service(db)
+    creds_service = get_credentials_service(db)
+
+    try:
+        order = order_service.get_order_or_raise(vendor_id, order_id)
+    except OrderNotFoundError:
+        raise ResourceNotFoundException("LetzshopOrder", str(order_id))
+
+    # Get inventory unit IDs from order
+    if not order.inventory_units:
+        return FulfillmentOperationResponse(
+            success=False,
+            message="No inventory units found in order",
+        )
+
+    inventory_unit_ids = [u.get("id") for u in order.inventory_units if u.get("id")]
+
+    if not inventory_unit_ids:
+        return FulfillmentOperationResponse(
+            success=False,
+            message="No inventory unit IDs found in order",
+        )
+
+    try:
+        with creds_service.create_client(vendor_id) as client:
+            result = client.confirm_inventory_units(inventory_unit_ids)
+
+            if not result.get("inventoryUnits"):
+                error_messages = [
+                    e.get("message", "Unknown error")
+                    for e in result.get("errors", [])
+                ]
+                return FulfillmentOperationResponse(
+                    success=False,
+                    message="Some inventory units could not be confirmed",
+                    errors=error_messages,
+                )
+
+            # Update order status
+            order_service.mark_order_confirmed(order)
+            db.commit()
+
+            return FulfillmentOperationResponse(
+                success=True,
+                message=f"Confirmed {len(inventory_unit_ids)} inventory units",
+                confirmed_units=[u.get("id") for u in result.get("inventoryUnits", [])],
+            )
+
+    except LetzshopClientError as e:
+        return FulfillmentOperationResponse(success=False, message=str(e))
+
+
+@router.post(
+    "/vendors/{vendor_id}/orders/{order_id}/reject",
+    response_model=FulfillmentOperationResponse,
+)
+def reject_order(
+    vendor_id: int = Path(..., description="Vendor ID"),
+    order_id: int = Path(..., description="Order ID"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Decline all inventory units for a Letzshop order.
+
+    Sends confirmInventoryUnits mutation with isAvailable=false for all items.
+    """
+    order_service = get_order_service(db)
+    creds_service = get_credentials_service(db)
+
+    try:
+        order = order_service.get_order_or_raise(vendor_id, order_id)
+    except OrderNotFoundError:
+        raise ResourceNotFoundException("LetzshopOrder", str(order_id))
+
+    # Get inventory unit IDs from order
+    if not order.inventory_units:
+        return FulfillmentOperationResponse(
+            success=False,
+            message="No inventory units found in order",
+        )
+
+    inventory_unit_ids = [u.get("id") for u in order.inventory_units if u.get("id")]
+
+    if not inventory_unit_ids:
+        return FulfillmentOperationResponse(
+            success=False,
+            message="No inventory unit IDs found in order",
+        )
+
+    try:
+        with creds_service.create_client(vendor_id) as client:
+            result = client.reject_inventory_units(inventory_unit_ids)
+
+            if not result.get("inventoryUnits"):
+                error_messages = [
+                    e.get("message", "Unknown error")
+                    for e in result.get("errors", [])
+                ]
+                return FulfillmentOperationResponse(
+                    success=False,
+                    message="Some inventory units could not be declined",
+                    errors=error_messages,
+                )
+
+            # Update order status
+            order_service.mark_order_rejected(order)
+            db.commit()
+
+            return FulfillmentOperationResponse(
+                success=True,
+                message=f"Declined {len(inventory_unit_ids)} inventory units",
+            )
+
+    except LetzshopClientError as e:
+        return FulfillmentOperationResponse(success=False, message=str(e))
+
+
+@router.post(
+    "/vendors/{vendor_id}/orders/{order_id}/items/{item_id}/confirm",
+    response_model=FulfillmentOperationResponse,
+)
+def confirm_single_item(
+    vendor_id: int = Path(..., description="Vendor ID"),
+    order_id: int = Path(..., description="Order ID"),
+    item_id: str = Path(..., description="Inventory Unit ID"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Confirm a single inventory unit in an order.
+
+    Sends confirmInventoryUnits mutation with isAvailable=true for one item.
+    """
+    order_service = get_order_service(db)
+    creds_service = get_credentials_service(db)
+
+    try:
+        order = order_service.get_order_or_raise(vendor_id, order_id)
+    except OrderNotFoundError:
+        raise ResourceNotFoundException("LetzshopOrder", str(order_id))
+
+    try:
+        with creds_service.create_client(vendor_id) as client:
+            result = client.confirm_inventory_units([item_id])
+
+            if not result.get("inventoryUnits"):
+                error_messages = [
+                    e.get("message", "Unknown error")
+                    for e in result.get("errors", [])
+                ]
+                return FulfillmentOperationResponse(
+                    success=False,
+                    message="Failed to confirm item",
+                    errors=error_messages,
+                )
+
+            # Update local inventory unit state
+            order_service.update_inventory_unit_state(order, item_id, "confirmed_available")
+            db.commit()
+
+            return FulfillmentOperationResponse(
+                success=True,
+                message="Item confirmed",
+                confirmed_units=[item_id],
+            )
+
+    except LetzshopClientError as e:
+        return FulfillmentOperationResponse(success=False, message=str(e))
+
+
+@router.post(
+    "/vendors/{vendor_id}/orders/{order_id}/items/{item_id}/decline",
+    response_model=FulfillmentOperationResponse,
+)
+def decline_single_item(
+    vendor_id: int = Path(..., description="Vendor ID"),
+    order_id: int = Path(..., description="Order ID"),
+    item_id: str = Path(..., description="Inventory Unit ID"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Decline a single inventory unit in an order.
+
+    Sends confirmInventoryUnits mutation with isAvailable=false for one item.
+    """
+    order_service = get_order_service(db)
+    creds_service = get_credentials_service(db)
+
+    try:
+        order = order_service.get_order_or_raise(vendor_id, order_id)
+    except OrderNotFoundError:
+        raise ResourceNotFoundException("LetzshopOrder", str(order_id))
+
+    try:
+        with creds_service.create_client(vendor_id) as client:
+            result = client.reject_inventory_units([item_id])
+
+            if not result.get("inventoryUnits"):
+                error_messages = [
+                    e.get("message", "Unknown error")
+                    for e in result.get("errors", [])
+                ]
+                return FulfillmentOperationResponse(
+                    success=False,
+                    message="Failed to decline item",
+                    errors=error_messages,
+                )
+
+            # Update local inventory unit state
+            order_service.update_inventory_unit_state(order, item_id, "confirmed_unavailable")
+            db.commit()
+
+            return FulfillmentOperationResponse(
+                success=True,
+                message="Item declined",
+            )
+
+    except LetzshopClientError as e:
+        return FulfillmentOperationResponse(success=False, message=str(e))