fix(install-windows): don't let a missing Ollama process abort the last step

taskkill writes to stderr when the process isn't running, and with
$ErrorActionPreference = Stop PowerShell 5.1 promotes native stderr to a
terminating error (2>$null doesn't prevent it). The normal case -- Ollama not
running -- threw and printed a failure warning for work that had succeeded.
Uses Get-Process | Stop-Process instead.

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

install-windows.ps1

@@ -228,8 +228,16 @@ try {
         Remove-Item $ollamaAutostart -Force
         Write-OK "Removed Ollama login autostart"
     }
-    foreach ($img in @("ollama app.exe", "ollama.exe")) {
-        taskkill /F /T /IM $img 2>$null | Out-Null
+    # Get-Process, not taskkill: taskkill writes "ERROR: The process ... not
+    # found." to stderr when nothing is running, and with $ErrorActionPreference
+    # = Stop PowerShell 5.1 promotes a native command's stderr to a TERMINATING
+    # error. `2>$null` does not prevent that. So the ordinary case - Ollama
+    # simply is not running - aborted this whole block and printed the warning
+    # below, claiming the install could not configure something it had in fact
+    # already done. Cmdlets have no such trap.
+    foreach ($name in @("ollama app", "ollama")) {
+        Get-Process -Name $name -ErrorAction SilentlyContinue |
+            Stop-Process -Force -ErrorAction SilentlyContinue
     }
     Write-OK "Ollama set to manual start"
 } catch {