fix(backend): update conversation and schedule center schemas

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/app/schemas/conversation.py

@@ -1,5 +1,7 @@
-from pydantic import BaseModel
 from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel
 
 
 class MessageCreate(BaseModel):
@@ -37,6 +39,7 @@ class ChatRequest(BaseModel):
     conversation_id: str | None = None
     agent_id: str | None = None
     model_name: str | None = None
+    runtime: Literal["jarvis", "hermes"] | None = None
     file_ids: list[str] = []