Queue updater relaunch after app exit

[IgorWarzocha]

Summary

• use Electron app.relaunch with the staged executable
• let the current app finish shutdown before the replacement starts
• remove the detached-spawn grace heuristic

Root cause

The Restart action spawned the replacement while the current Electron process still owned the user-data lock. The replacement could start briefly and exit before the old process finished quitting. Electron app.relaunch queues the executable and starts it after the current instance exits.

Evidence

The laptop staged the new immutable hash successfully, then Restart left no app process. The replacement ran far enough to perform its startup wrapper migration before losing the handoff.

Validation

• full gate: 48 test files / 116 tests, React Doctor 100
• next dev release will be exercised by the currently installed repaired build