fix: detect real OS arch on Windows-on-ARM

PROCESSOR_ARCHITECTURE reports the current process's arch, not the
OS's. On ARM64 Windows, a PowerShell running under x64 emulation
would report AMD64, causing start-local-agent.ps1 to download the
x64 Node.js build even though an arm64 build is available. Fall
back to PROCESSOR_ARCHITEW6432, which holds the native OS arch
when the process itself is emulated.

Author: ouyyyyang

scripts/dev/start-local-agent.ps1

@@ -88,8 +88,16 @@ function Install-NodeLocal {
     Write-Host "This does NOT modify your system environment. Delete runtime\node\ to remove it."
     Write-Host ""
 
+    # PROCESSOR_ARCHITECTURE reports the current process's arch, not the OS.
+    # On Windows-on-ARM, a PowerShell running under x64 emulation reports AMD64
+    # here, so also check PROCESSOR_ARCHITEW6432 which holds the native OS arch
+    # when the process is emulated.
+    $procArch = $env:PROCESSOR_ARCHITECTURE
+    $nativeArch = $env:PROCESSOR_ARCHITEW6432
+    $osArch = if ($nativeArch) { $nativeArch } else { $procArch }
+
     $arch = if ([Environment]::Is64BitOperatingSystem) {
-        if ($env:PROCESSOR_ARCHITECTURE -eq "ARM64") { "arm64" } else { "x64" }
+        if ($osArch -eq "ARM64") { "arm64" } else { "x64" }
     } else { "x86" }
 
     $nodeVersion = "v22.16.0"