feat(install-windows): close the terminal at the end, since its PATH is stale

A process reads PATH once, at startup, so the shell the installer ran in can
never resolve ncp. The ending now says that and closes the window. Uses
Stop-Process -Id $PID rather than 'exit', which only closes the window when the
host was started with -File.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

install-windows.ps1

@@ -13,11 +13,11 @@
 
     Requires Windows 10/11 with winget (App Installer). No reboot needed.
 .PARAMETER OwnsWindow
-    Internal. Set only on the elevated run this script starts for itself, which
+    Internal. Set only on the elevated run this script starts for itself. That
-    gets a console window of its own - so it is allowed to close that window when
+    run has a console of its own, so a fatal error has to pause before the window
-    it finishes. Without it we assume we are a guest in someone's existing shell
+    disappears with the message on it. In a shell the user already had open the
-    and must not kill it (closing would take their session, and any transcript
+    text stays on screen, and a prompt there is a keystroke nobody asked for.
-    they were recording, with it). Not meant to be passed by hand.
+    Not meant to be passed by hand.
 #>
 param(
     [switch]$OwnsWindow
@@ -283,10 +283,22 @@ Write-Host "  The app opens at http://localhost:8000" -ForegroundColor White
 Write-Host "  The AI starts OFF - click 'Start AI' in the sidebar to turn it on." -ForegroundColor White
 Write-Host ""
 Write-Host "  Terminal:  open a NEW terminal (PowerShell or cmd), then run  ncp help" -ForegroundColor White
-Write-Host "             (PATH is read at process start, so open windows lack it)" -ForegroundColor DarkGray
 Write-Host "  ==========================================================" -ForegroundColor Green
 Write-Host ""
-if ($OwnsWindow) {
+Write-Host "  This window has to close for ncp to work." -ForegroundColor Yellow
-    Read-Host "Press Enter to close"
+Write-Host "  A process reads PATH once, when it starts. This shell started before" -ForegroundColor DarkGray
-    exit 0    # -File means the script ending ends powershell.exe, closing the window
+Write-Host "  the installer put management\ on PATH, so it will never see ncp no" -ForegroundColor DarkGray
-}
+Write-Host "  matter what you run here. The next terminal you open will." -ForegroundColor DarkGray
+Write-Host ""
+Read-Host "  Press Enter to close this window (Ctrl+C works too)"
+
+# Stop-Process on our own PID, not `exit`: `exit` only ends the window when the
+# host was started with -File. Run interactively - `& .\install-windows.ps1` from
+# a shell already open, which is the common case - it would just return to the
+# prompt in a session whose PATH is permanently stale. Killing the host closes
+# the window either way, which is the point: the user cannot accidentally keep
+# using a shell where ncp will never resolve.
+# Caveat: a Start-Transcript in this window never reaches Stop-Transcript. The
+# transcript is flushed as it is written, so the content survives without the
+# closing footer.
+Stop-Process -Id $PID