Fix: pass tool_call_id through to watsonx API

watsonx requires tool_call_id on role=tool messages.
Added field to ChatMessage model and passthrough in transformer.

app/utils/transformers.py

@@ -47,6 +47,9 @@ def transform_messages_to_watsonx(messages: List[ChatMessage]) -> List[Dict[str,
         if msg.function_call:
             watsonx_msg["function_call"] = msg.function_call
         
+        if msg.tool_call_id:
+            watsonx_msg["tool_call_id"] = msg.tool_call_id
+        
         watsonx_messages.append(watsonx_msg)
     
     return watsonx_messages