Build the SecureString for an inline key on Windows too

The vault is written with ConvertFrom-SecureString -SecureString, so the
inline branch has to produce a SecureString as well - it only set the
plain text, and under Set-StrictMode the vault write then failed with
'the variable $secure cannot be retrieved'. Caught by running the new
form on the Windows box rather than assuming it.

Co-Authored-By: Claude Code <noreply@anthropic.com>

claude-mode.ps1

@@ -380,6 +380,9 @@ function Set-VaultKey {
     if ($Key) {
         Write-Warn2 'the key was given on the command line, so it is in this shell history - the hidden prompt leaves no trace'
         $plain  = $Key
+        # The vault is written from a SecureString (DPAPI), so the inline form
+        # has to produce one too.
+        $secure = ConvertTo-SecureString -String $Key -AsPlainText -Force
     } else {
         Write-Host "Paste the API key for ref '$Ref' (input hidden):"
         $secure = Read-Host -AsSecureString