Revert "fix: remove redudant export for client plugin"

This reverts commit 48b259100b9cfe2e372eb9fe0924a783988f5a8e.

packages/client/ui-sidebar/tests/tree.spec.ts

@@ -3,7 +3,7 @@ import type { SessionId, SessionListState, SessionSummary } from '@deepseek-ai/d
 import {
   deriveRows, formatRelativeTime, projectLabel, UNGROUPED_KEY, UNGROUPED_LABEL,
   type SessionRow, type TreeView,
-} from '../src/client/tree.ts'
+} from '@deepseek-ai/dsh-client-ui-sidebar/client'
 
 const sid = (s: string) => s as SessionId