Fix mypy type error on mcp_servers list

Add explicit union type annotation so mypy accepts both
MCPServerStreamableHttp and MCPServerStdio in the same list.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: John-Lin

bot/agents.py

@@ -88,7 +88,7 @@ def truncate_history(self, chat_id: int) -> None:
 
     @classmethod
     def from_dict(cls, name: str, config: dict[str, Any]) -> OpenAIAgent:
-        mcp_servers = []
+        mcp_servers: list[MCPServerStreamableHttp | MCPServerStdio] = []
         for mcp_srv in config.get("mcpServers", {}).values():
             if "httpUrl" in mcp_srv:
                 mcp_servers.append(