Add debugging to investigate account mapping issues

Debug Features:
- Added debug output to show what form data is being submitted
- Shows which lines have data and which are empty/not set
- Helps identify if Dolibarr multiselectarray sends empty arrays
- Will help diagnose why accounts are being lost

This will help us understand what's happening with the form submission!

admin/setup_mvp.php

@@ -40,15 +40,25 @@ if ($action == 'update_mappings') {
     $ca3_definitions = $config->getCA3LineDefinitions();
     $updated_count = 0;
     
+    // Debug: Show what's being submitted
+    $debug_info = array();
+    foreach ($ca3_definitions as $line => $definition) {
+        $account_codes = GETPOST('account_codes_' . $line, 'array');
+        $debug_info[] = "$line: " . (is_array($account_codes) ? implode(',', $account_codes) : 'not set');
+    }
+    setEventMessages("Debug: Form data - " . implode(' | ', $debug_info), null, 'warnings');
+    
     foreach ($ca3_definitions as $line => $definition) {
         $account_codes = GETPOST('account_codes_' . $line, 'array');
         
-        // Process all lines, even empty ones (to clear mappings)
+        // Process all lines that have form data
+        if (isset($_POST['account_codes_' . $line])) {
             $result = $config->updateAccountMapping($line, $account_codes);
             if ($result) {
                 $updated_count++;
             }
         }
+    }
     
     if ($updated_count > 0) {
         setEventMessages($langs->trans("ConfigurationUpdated"), null, 'mesgs');