[Bug]: Preset creation stalls because the machine goes to sleep #4202

Steps to reproduce

1. Start preset creation and leave the machine alone (MacBook, default sleep settings):
2. Come back a few hours later.

Actual behaviour

The CLI has printed, more than once:

Agent process exited without a report; resuming in 30s.

The machine went to sleep. macOS entered Idle Sleep.

Nothing in dstack keeps the machine awake for the duration. Claude Code's own session runtime holds a renewable PreventUserIdleSystemSleep assertion while it works, but the headless claude -p agent that preset creation spawns holds none, and neither does the dstack apply process, which sits in the foreground for the whole session doing nothing but supervise it. Preset creation is built for long unattended runs, with resume, a retry budget, and reconciliation, so having it defeated by the machine idling is surprising. dstack preset creation should run caffeinate.

Expected behavior

A creation session keeps the machine awake for as long as it runs. Observed on macOS; the same class of problem presumably exists on other platforms.