fix(vpn): give the QR code the specified four-module quiet zone

Two modules is below the minimum, and against a bordered card some readers fail
to locate the symbol at all.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/Services/Wireguard/QrCode.php

@@ -21,7 +21,9 @@ final class QrCode
         // against a screen — more redundancy would only make the code denser.
         $matrix = Encoder::encode($text, ErrorCorrectionLevel::L())->getMatrix();
         $width = $matrix->getWidth();
-        $quiet = 2;
+        // Four modules is the specified minimum quiet zone. Less than that and
+        // some readers fail to find the symbol at all against a bordered card.
+        $quiet = 4;
         $total = $width + 2 * $quiet;
 
         $cells = '';