Mirror the bootstrap-installer (Rust) fix in the Electron first-launch
runner. spawnPowerShell launched bare 'powershell.exe', trusting PATH to
contain %SystemRoot%\System32\WindowsPowerShell\v1.0 — the same latent
weakness that stalled the native installer at "0 of 0 steps" when PATH is
trimmed/truncated or stored as a non-expanding REG_SZ. Resolve by absolute
path first (%SystemRoot%/%windir%), then PATH (powershell 5.1 -> pwsh 7),
then bare name as last resort.
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