Remove websocket streaming and unused kernel creation

Deleted the websocket_streaming.py module and removed the create_kernel method from AppConfig, as the system now uses Azure AI Agent Project pattern. Added placeholder files for messages_af.py and utils_af.py to support future Azure Foundry integration.

Author: Fr4nc3

src/backend/common/config/app_config.py

@@ -7,7 +7,7 @@
 from azure.cosmos import CosmosClient
 from azure.identity import DefaultAzureCredential, ManagedIdentityCredential
 from dotenv import load_dotenv
-from semantic_kernel import Kernel
+
 
 # Load environment variables from .env file
 load_dotenv()
@@ -215,17 +215,6 @@ def get_cosmos_database_client(self):
             )
             raise
 
-    def create_kernel(self):
-        """Creates a new Semantic Kernel instance.
-
-        Returns:
-            A new Semantic Kernel instance
-        """
-        # Create a new kernel instance without manually configuring OpenAI services
-        # The agents will be created using Azure AI Agent Project pattern instead
-        kernel = Kernel()
-        return kernel
-
     def get_ai_project_client(self):
         """Create and return an AIProjectClient for Azure AI Foundry using from_connection_string.