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/Cleanup-OrphanedBuildVMs.ps1

@@ -37,7 +37,7 @@
 param(
     [string] $CloneBaseDir = 'F:\CI\BuildVMs',
 
-    [ValidateRange(1, 168)]
+    [ValidateRange(0, 168)]
     [int] $MaxAgeHours = 4,
 
     [string] $VmrunPath = 'C:\Program Files (x86)\VMware\VMware Workstation\vmrun.exe'
@@ -102,3 +102,17 @@ foreach ($dir in $orphans) {
 }
 
 Write-Host "[Cleanup] Done."
+
+# ── Stale vm-start.lock cleanup ─────────────────────────────────────────────
+# The lock is released by Invoke-CIJob.ps1 normally. On host crash it persists
+# and causes a confusing 10-minute retry loop on the next job. Remove if older
+# than 30 minutes.
+$lockFile   = 'F:\CI\State\vm-start.lock'
+$lockCutoff = (Get-Date).AddMinutes(-30)
+if ((Test-Path $lockFile) -and (Get-Item $lockFile).LastWriteTime -lt $lockCutoff) {
+    if ($PSCmdlet.ShouldProcess($lockFile, 'Remove stale vm-start.lock')) {
+        $ageMin = [int]((Get-Date) - (Get-Item $lockFile).LastWriteTime).TotalMinutes
+        Remove-Item $lockFile -Force -ErrorAction SilentlyContinue
+        Write-Host "[Cleanup] Removed stale vm-start.lock (age: ${ageMin} min)"
+    }
+}