feat(sprint3): Invoke-VmrunBounded, Get-GuestIPAddress, transport and concurrency hardening

H4: Invoke-VmrunBounded added to _Common.psm1 (Start-Process + Wait-Process + taskkill on
    timeout, returns {ExitCode;Output;TimedOut;ElapsedSeconds}). Wired in Invoke-CIJob.ps1
    for vmrun start (180s) and Remove-BuildVM.ps1 for stop/deleteVM (60s/90s).
H5: Cleanup-OrphanedBuildVMs.ps1 removes stale vm-start.lock (>30 min). ValidateRange
    lowered to 0 to allow emergency -MaxAgeHours 0. Invoke-RetentionPolicy.ps1 same.
H8: _Transport.psm1 SSH hardening: StrictHostKeyChecking=accept-new, F:\CI\State\known_hosts.
H9: Validate-DeployState.ps1 Linux branch added: checks ci-report-ip.service enabled,
    ci-report-ip.sh executable via SSH. New params: -GuestOS, -SshKeyPath, -SshUser.
H12: Get-GuestIPAddress extracted into _Common.psm1 (guestinfo.ci-ip primary, getGuestIPAddress
     fallback). Invoke-CIJob.ps1 Phase 3b replaced with single call. Measure-CIBenchmark.ps1
     updated to match.
Also: _Common.psm1 adds Write-CIRedactedCommand and ConvertTo-SafeShellSingleQuotedString.
     Pester suite updated: 30/30 pass.

scripts/Measure-CIBenchmark.ps1

@@ -130,23 +130,11 @@ for ($i = 1; $i -le $Iterations; $i++) {
         $t.start = [math]::Round($sw.Elapsed.TotalSeconds, 2)
         Write-Host "[bench] start: $($t.start)s"
 
-        # ── Phase: IP acquire (poll getGuestIPAddress) ────────────────────────
+        # ── Phase: IP acquire (primary: guestinfo.ci-ip, fallback: getGuestIPAddress) ──
         Write-Host "[bench] Waiting for guest IP..."
         $sw.Restart()
-        $deadline = (Get-Date).AddSeconds($TimeoutSeconds)
-        $vmIP     = $null
-        while ((Get-Date) -lt $deadline) {
-            $ipResult = Invoke-Vmrun -VmrunPath $VmrunPath -Operation getGuestIPAddress `
-                            -Arguments @($cloneVmx)
-            if ($ipResult.ExitCode -eq 0) {
-                $candidate = "$($ipResult.Output)".Trim()
-                if ($candidate -match '^\d+\.\d+\.\d+\.\d+$') {
-                    $vmIP = $candidate
-                    break
-                }
-            }
-            Start-Sleep -Seconds 3
-        }
+        $vmIP = Get-GuestIPAddress -VmrunPath $VmrunPath -VmxPath $cloneVmx `
+                    -TimeoutSeconds $TimeoutSeconds
         if (-not $vmIP) { throw "Timed out waiting for guest IP after $TimeoutSeconds s" }
         $t.ip   = [math]::Round($sw.Elapsed.TotalSeconds, 2)
         $t.vmIP = $vmIP