fix: strip markdown hard-break backslashes from webhook payloads (#13950)

app/services/messages/webhook_content_normalizer.rb

@@ -0,0 +1,10 @@
+# Strips CommonMark hard line breaks from stored markdown source (backslash before newline).
+# ProseMirror / the dashboard editor emits this form so soft breaks survive as markdown;
+# webhook consumers expect plain newlines without a visible backslash (e.g. WhatsApp gateways).
+class Messages::WebhookContentNormalizer
+  def self.normalize(text)
+    return text if text.blank?
+
+    text.gsub(/\\\r?\n/, "\n")
+  end
+end