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

backend/wb_api/__init__.py

@@ -0,0 +1,15 @@
+from .client import WBClient
+from .services.content import ContentService
+from .services.marketplace import MarketplaceService
+
+class WildberriesAPI:
+    """
+    Main entry point for Wildberries SDK.
+    Instantiates all services with a shared client.
+    """
+    def __init__(self, api_token: str = None):
+        self.client = WBClient(api_token)
+        
+        # Initialize services
+        self.content = ContentService(self.client)
+        self.marketplace = MarketplaceService(self.client)