fix(onboarding): point the import hint at the group command for multi-agent history

With several agents' history pending, the single 'run later' hint named only the first agent's import subcommand, so following it looked like the whole import step was resolved. Keep the direct subcommand for one agent; point at 'entire import' (which lists the per-agent subcommands) for several.

Trail-Finding: 019f6822-9c6f-7efa-979c-e2b3cd87598b