Fallback unknown signature styles when saving preferences

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "linkedsign-backend",
-  "version": "1.2.19",
+  "version": "1.2.20",
   "private": true,
   "description": "Initial backend for LinkedSign",
   "main": "src/server.js",

backend/src/modules/users/users.service.js

@@ -16,11 +16,9 @@ const getSignaturePreferences = async (userId) => {
 
 const updateSignaturePreferences = async (userId, { signatureStyle, qrPosition, qrBackground, qrBorder, signatureImageBase64 }) => {
   const rawSignatureStyle = String(signatureStyle || '').trim().toLowerCase();
-  const normalizedSignatureStyle = LEGACY_SIGNATURE_STYLE_MAP[rawSignatureStyle] || rawSignatureStyle || 'qr';
+  let normalizedSignatureStyle = LEGACY_SIGNATURE_STYLE_MAP[rawSignatureStyle] || rawSignatureStyle || 'qr';
   if (!ALLOWED_SIGNATURE_STYLES.includes(normalizedSignatureStyle)) {
-    const error = new Error('Invalid signature style.');
-    error.statusCode = 400;
-    throw error;
+    normalizedSignatureStyle = rawSignatureStyle.includes('firma') ? 'firmaec' : 'qr';
   }
 
   // Preferences should be resilient to stale clients or partially populated forms.