feat: add manual "转人工" (request human) action for conversations

- Backend: RequestHuman service method changes status from AI_SERVING to PENDING
- Backend: POST /api/dashboard/conversation/request-human endpoint
- Frontend: requestHumanConversation API client
- Frontend: "转人工" button in conversation list dropdown and detail dialog

web/app/dashboard/conversation-monitor/_components/detail.tsx

@@ -40,7 +40,8 @@ type ConversationDetailDialogProps = {
   onLoadMoreMessages?: () => void | Promise<void>;
   onOpenChange: (open: boolean) => void;
   onOpenAssign: () => void;
-  onDispatch: () => Promise<void>;
+  onDispatch: () => Promise<void>
+  onRequestHuman?: () => Promise<void>;
   onOpenTransfer: () => void;
   onRead: () => Promise<void>;
   onOpenClose: () => void;
@@ -272,6 +273,14 @@ export function ConversationDetailDialog({
               : "暂无会话信息"}
           </div>
           <div className="flex flex-wrap gap-2">
+            <Button
+              variant="outline"
+              onClick={() => void onRequestHuman?.()}
+              disabled={saving || !currentConversation || currentConversation.status !== 1}
+            >
+              <MessageCircleMoreIcon />
+              {saving ? "处理中..." : "转人工"}
+            </Button>
             <Button
               variant="outline"
               onClick={onOpenAssign}