fix(install.ps1): replace Write-Error+exit with throw in Die()

With $ErrorActionPreference='Stop', Write-Error throws immediately and
exit 1 is dead code. More critically, exit 1 in an irm|iex session
would close the user's interactive PowerShell window if it were reached.

throw gives a clean single-line error message and is safe for
embedded execution via irm|iex.

Author: cderv

install.ps1

@@ -36,7 +36,7 @@ $Repo = 'q2'
 $Platform = 'windows_amd64'
 $UA = @{ 'User-Agent' = 'q2-install' }
 
-function Die([string]$msg) { Write-Error "q2 install: $msg"; exit 1 }
+function Die([string]$msg) { throw "q2 install: $msg" }
 function Step([string]$msg) { Write-Host "-> $msg" }
 
 # q2 ships an x86_64 Windows binary; ARM64 Windows runs it under