fix(diagnostics): use StrictHostKeyChecking=no for Linux guest-diag SSH

Diagnostics is best-effort. Using accept-new without UserKnownHostsFile
caused the system known_hosts (~/.ssh/known_hosts) to be consulted,
which holds a stale key from a previous clone of the same IP.
Switch to no+NUL (same as Wait-VMReady) to avoid false host-key errors.

scripts/_Common.psm1

@@ -391,7 +391,8 @@ function Get-GuestDiagnostics {
             Write-Warning "[Diagnostics] No SshKeyPath supplied for Linux guest — skipping."
             return
         }
-        $sshOpts = @('-i', $SshKeyPath, '-o', 'StrictHostKeyChecking=accept-new',
+        $sshOpts = @('-i', $SshKeyPath, '-o', 'StrictHostKeyChecking=no',
+                     '-o', 'UserKnownHostsFile=NUL',
                      '-o', 'ConnectTimeout=10', '-o', 'BatchMode=yes')
         try {
             # Collect: journalctl errors, ps, df