refactor(message): return MessageRead schema instead of raw model

Convert the return type of create_messages_for_turn to use MessageRead schema for better data encapsulation and consistency with API responses.

db/crud/message.py

@@ -5,6 +5,7 @@ from datetime import datetime, timezone
 
 from db.models.chat import Chat
 from db.models.message import Message
+from db.schemas.message import MessageRead
 from langchain_core.messages import BaseMessage, HumanMessage, AIMessage, ToolMessage
 
 
@@ -14,7 +15,7 @@ async def create_messages_for_turn(
     new_lc_messages: list[BaseMessage],
     final_answer: str,
     links: list[str],
-) -> Message:
+) -> MessageRead:
     """
     Creates all new messages generated during a single agent turn.
 
@@ -31,7 +32,7 @@ async def create_messages_for_turn(
         links: The list of parsed source links from the agent's output.
 
     Returns:
-        The final AI Message
+        The final AI Message, converted to a MessageRead schema.
     """
     # First, get the parent chat to update its timestamp.
     # This also ensures the chat exists before we try to add messages to it.
@@ -76,11 +77,11 @@ async def create_messages_for_turn(
     db.add_all(db_messages_to_add)
     await db.commit()
 
-    # Only refresh the single message we need to return to the client.
     final_ai_message = db_messages_to_add[-1]
     await db.refresh(final_ai_message)
-
-    return final_ai_message
+    
+    # Return the final AI message as a MessageRead schema
+    return MessageRead.model_validate(final_ai_message)
 
 
 async def get_messages_by_chat(db: AsyncSession, chat_id: uuid.UUID) -> list[Message]: