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

backend/ozon_api/services/fbs.py

@@ -0,0 +1,33 @@
+from typing import Dict, Any, List
+from ..client import OzonClient
+
+class FBSService:
+    """Service to handle FBS (Fulfillment by Seller) operations."""
+    
+    def __init__(self, client: OzonClient):
+        self.client = client
+
+    def get_unfulfilled_list(self, dir: str = "ASC", filter_params: Dict[str, Any] = None, limit: int = 100, offset: int = 0) -> Dict[str, Any]:
+        """
+        Get a list of new/unfulfilled FBS orders.
+        Endpoint: /v3/posting/fbs/unfulfilled/list
+        """
+        payload = {
+            "dir": dir,
+            "filter": filter_params or {},
+            "limit": limit,
+            "offset": offset,
+            "with": {
+                "analytics_data": True,
+                "barcodes": True,
+                "financial_data": True
+            }
+        }
+        return self.client.post("/v3/posting/fbs/unfulfilled/list", data=payload)
+
+    def ship_packages(self, packages: List[Dict[str, Any]]) -> Dict[str, Any]:
+        """
+        Ship unfulfilled orders.
+        Endpoint: /v3/posting/fbs/ship
+        """
+        return self.client.post("/v3/posting/fbs/ship", data={"packages": packages})