Suspend idle Local VMs safely

[milind-soni]

Summary

• automatically stop a running Local VM after 8 hours without activity
• renew the idle window for bot runtime events, VM starts, and preview screenshots
• restore the timer for a VM that survived an app restart
• defer suspension while a bot turn or lifecycle operation is active
• cancel the timer after an explicit stop or removal
• explain the behavior in Local VM settings

The backstop only stops the container. It never removes the VM, image, or durable workspace, so starting again is reversible.

Verification

• pnpm test (457 passed, 8 skipped; updater tests 11 passed)
• pnpm build
• deterministic timer tests cover renewal, active-work deferral, cancellation, and retry after transient failure

Merge order

This is stacked on #155. Merge #151, #153, #154, #155, then this PR.

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[milind-soni]

Superseded by #158, which reapplies this change cleanly on current main and has now merged.