feat(linux): update orchestration scripts for dual-OS (Windows/Linux) support

Wait-VMReady.ps1:
- Phase 1: vmrun list + path matching instead of getGuestIPAddress (avoids hang)
- Phase 2/3: WinRM (Windows) or TCP:22 + ssh echo (Linux) based on -Transport param
- -Transport SSH auto-selected by Invoke-CIJob when guestOS=ubuntu-64

Invoke-CIJob.ps1:
- Auto-detect GuestOS from clone VMX guestOS field
- Pass -GuestOS Linux to Wait-VMReady, Invoke-RemoteBuild, Get-BuildArtifacts
- Git clone output streamed line-by-line (fix buffered stdout)

Invoke-RemoteBuild.ps1:
- -GuestOS Linux path: SSH+SCP via _Transport.psm1
- Always uses in-VM git clone for Linux builds

Get-BuildArtifacts.ps1:
- -GuestOS Linux path: scp -r ci_build@<ip>:/opt/ci/output/ to host artifact dir

scripts/Get-BuildArtifacts.ps1

@@ -42,7 +42,7 @@ param(
     [ValidatePattern('^((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$')]
     [string] $IPAddress,
 
-    [Parameter(Mandatory)]
+    [Parameter()]
     [System.Management.Automation.PSCredential] $Credential,
 
     [Parameter(Mandatory)]
@@ -51,7 +51,17 @@ param(
     [Parameter(Mandatory)]
     [string] $HostArtifactDir,
 
-    [switch] $IncludeLogs
+    [switch] $IncludeLogs,
+
+    # Guest OS type — Linux uses SCP instead of WinRM.
+    [ValidateSet('Windows', 'Linux')]
+    [string] $GuestOS = 'Windows',
+
+    # SSH private key path (used when GuestOS=Linux).
+    [string] $SshKeyPath = 'F:\CI\keys\ci_linux',
+
+    # SSH username (used when GuestOS=Linux).
+    [string] $SshUser = 'ci_build'
 )
 
 Set-StrictMode -Version Latest
@@ -59,6 +69,38 @@ $ErrorActionPreference = 'Stop'
 
 Import-Module (Join-Path $PSScriptRoot '_Common.psm1') -Force
 
+if ($GuestOS -eq 'Windows' -and $null -eq $Credential) {
+    throw "Credential is required when GuestOS is Windows."
+}
+
+# ── Linux branch: use scp to transfer artifacts ─────────────────────────────────────────────
+if ($GuestOS -eq 'Linux') {
+    Import-Module (Join-Path $PSScriptRoot '_Transport.psm1') -Force
+
+    if (-not (Test-Path $HostArtifactDir)) {
+        New-Item -ItemType Directory -Path $HostArtifactDir -Force | Out-Null
+        Write-Host "[Get-BuildArtifacts] Created host artifact directory: $HostArtifactDir"
+    }
+
+    Write-Host "[Get-BuildArtifacts] Transferring artifacts via SCP from $GuestArtifactPath ..."
+
+    Copy-SshItem `
+        -Source      "$GuestArtifactPath/." `
+        -Destination $HostArtifactDir `
+        -IP          $IPAddress `
+        -User        $SshUser `
+        -KeyPath     $SshKeyPath `
+        -Direction   'FromGuest' `
+        -Recurse
+
+    $transferred = @(Get-ChildItem -Path $HostArtifactDir -Recurse -File -ErrorAction SilentlyContinue)
+    if ($transferred.Count -eq 0) {
+        throw "[Get-BuildArtifacts] No files found in $HostArtifactDir after SCP transfer."
+    }
+    Write-Host "[Get-BuildArtifacts] $($transferred.Count) file(s) collected from Linux guest."
+    return
+}
+
 # Ensure destination exists on host
 if (-not (Test-Path $HostArtifactDir)) {
     New-Item -ItemType Directory -Path $HostArtifactDir -Force | Out-Null