fix: replace backtick-n with [Environment]::NewLine in PS script

Go raw strings (backtick-delimited) cannot contain backticks, so
PowerShell's backtick-n newline literal breaks the Go compiler.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

edge-ai-platform/installer/platform_windows.go

@@ -189,12 +189,12 @@ try {
 
     # Step 3: Install driver via pnputil
     $pnpResult = & pnputil.exe /add-driver '%s' /install 2>&1
-    $pnpText = $pnpResult -join "`n"
+    $pnpText = $pnpResult -join [Environment]::NewLine
 
     # If pnputil failed with signature error, try with /force (Windows 11 23H2+)
     if ($LASTEXITCODE -ne 0 -and $pnpText -match '簽章|signature|sign') {
         $pnpResult = & pnputil.exe /add-driver '%s' /install /force 2>&1
-        $pnpText = $pnpResult -join "`n"
+        $pnpText = $pnpResult -join [Environment]::NewLine
     }
 
     # Cleanup cert file