examples/sandboxy: fix misleading --name "resume" messaging

[moollaza]

Problem

When a session ends, sandboxy run prints:

Instance <name> saved. Resume with: sandboxy run --name <name> <agent>

This is misleading: --name boots the VM from the preserved rootfs, but the agent is launched from its definition's plain launchCommand plus passthrough args, so every run starts a fresh conversation. A user following the printed hint verbatim gets a new conversation each time and can reasonably conclude their history was lost.

Conversation state lives agent-side — e.g. cline stores sessions under ~/.cline (which its agent definition mounts from the host) — and resumes via the agent's own flag, independent of --name:

sandboxy run cline --id <session-id>    # `cline history` lists session ids

Change

One word: "Resume with:" → "Reuse with:", so the status line says what the command actually does. No behavior change.

Testing

• make build; ran a sandboxed agent session end-to-end and confirmed the corrected status line prints.
• Verified on a real machine that resume-via-agent-flag works: resuming a cline conversation with --id picks up the full transcript through the host-mounted ~/.cline.