Mark or unmark a conversation

Conversation marking is a Commercial capability commonly used with a marked conversation group. The frozen UTS contract has neither a markConversation operation nor an isMarked field in OpenIMSetConversationParams.

The client therefore cannot simulate a mark through ex or another field. Use a supported commercial business backend or confirmed upper-layer service, then refresh the conversation list and conversation groups.

When no real write API is available, hide or disable the action instead of changing local-only state that will disappear on the next query.