fix(pc-client): 会话置顶改用 SDK setConversation

@openim/electron-client-sdk 无 pinConversation，右键置顶会 TS2551 且运行时 TypeError。改走已有的 setConversation，删除路径不动。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

pc-client/src/pages/chat/ConversationSider/ConversationItem.tsx

@@ -55,7 +55,7 @@ const ConversationItem = ({ isActive, conversation }: IConversationProps) => {
   const onMenuClick = async ({ key }: { key: string }) => {
     try {
       if (key === "pin") {
-        await IMSDK.pinConversation({
+        await IMSDK.setConversation({
           conversationID: conversation.conversationID,
           isPinned: !conversation.isPinned,
         });