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

backend/wb_api/services/content.py

@@ -0,0 +1,39 @@
+from typing import Dict, Any, List
+from ..client import WBClient
+
+class ContentService:
+    """Service to handle WB product cards (Content API)."""
+    
+    def __init__(self, client: WBClient):
+        self.client = client
+        self.base_url = WBClient.CONTENT_API
+
+    def get_cards_list(self, limit: int = 100, updated_at: str = "", last_id: str = "") -> Dict[str, Any]:
+        """
+        Get list of nomenclatures (product cards).
+        Endpoint: /content/v2/get/cards/list
+        """
+        payload = {
+            "settings": {
+                "cursor": {
+                    "limit": limit
+                },
+                "filter": {
+                    "withPhoto": -1
+                }
+            }
+        }
+        
+        if updated_at:
+            payload["settings"]["cursor"]["updatedAt"] = updated_at
+        if last_id:
+            payload["settings"]["cursor"]["nmID"] = int(last_id)
+            
+        return self.client.post(self.base_url, "/content/v2/get/cards/list", data=payload)
+
+    def create_cards(self, cards: List[Dict[str, Any]]) -> Dict[str, Any]:
+        """
+        Create product cards.
+        Endpoint: /content/v2/cards/upload
+        """
+        return self.client.post(self.base_url, "/content/v2/cards/upload", data=cards)