feat: implement backend API clients for multi-marketplace integration and frontend service layer

backend/mm_api/services/orders.py

@@ -0,0 +1,52 @@
+from typing import Dict, Any, List
+from ..client import MMClient
+
+class OrdersService:
+    """Service to handle Magnit Market Orders (FBS)."""
+    
+    def __init__(self, client: MMClient):
+        self.client = client
+
+    def get_unprocessed_list(self, dir: str = "ASC", page_size: int = 100, page_token: str = None, **filters) -> Dict[str, Any]:
+        """
+        Get list of unprocessed assembly tasks.
+        Endpoint: /api/seller/v1/orders/list/unprocessed
+        """
+        payload = {
+            "dir": dir,
+            "page_size": page_size
+        }
+        if page_token:
+            payload["page_token"] = page_token
+            
+        # Add any extra filters like created_at, cutoff_time, etc.
+        payload.update(filters)
+        
+        return self.client.post("/api/seller/v1/orders/list/unprocessed", data=payload)
+
+    def get_list(self, dir: str = "ASC", page_size: int = 100, page_token: str = None, **filters) -> Dict[str, Any]:
+        """
+        Get list of orders by parameters.
+        Endpoint: /api/seller/v1/orders/list
+        """
+        payload = {
+            "dir": dir,
+            "page_size": page_size
+        }
+        if page_token:
+            payload["page_token"] = page_token
+            
+        payload.update(filters)
+        
+        return self.client.post("/api/seller/v1/orders/list", data=payload)
+
+    def cancel_items(self, order_id: str, items: List[Dict[str, int]]) -> Dict[str, Any]:
+        """
+        Cancel specific items in an order.
+        Endpoint: /api/seller/v1/orders/cancel-items
+        """
+        payload = {
+            "order_id": order_id,
+            "items": items
+        }
+        return self.client.post("/api/seller/v1/orders/cancel-items", data=payload)