[core] fix: strip escaped newlines from ChatWoot v4.10.1+ messages (#1900)

ChatWoot v4.10.1 escapes newlines by prepending a trailing backslash
before each line break in webhook payloads. This caused literal
backslash characters to appear in WhatsApp messages.

Strip the trailing backslash before newlines in MarkdownToWhatsApp()
so line breaks are preserved correctly.

Closes #1833
Mentions chatwoot/chatwoot#13348

Co-authored-by: Dani Lipari <dani.lipari@dontouch.ch>

src/apps/chatwoot/messages/to/whatsapp/markdown.test.ts

@@ -15,6 +15,12 @@ describe('MarkdownToWhatsApp', () => {
     expect(MarkdownToWhatsApp(input)).toBe(expected);
   });
 
+  // ChatWoot v4.10.1+ escapes newlines with trailing backslash
+  it('strips trailing backslash before newlines', () => {
+    const input = 'Hi \\\ntext message \\\nwith line \\\nbreak';
+    expect(MarkdownToWhatsApp(input)).toBe('Hi \ntext message \nwith line \nbreak');
+  });
+
   // Tests for URL protection
   it('preserves URLs with multiple underscores', () => {
     const input = 'https://example.com/page__name__test';

src/apps/chatwoot/messages/to/whatsapp/markdown.ts

@@ -4,6 +4,8 @@ export function MarkdownToWhatsApp(text: string): string {
   }
   return (
     text
+      // Remove trailing backslash before newlines (ChatWoot v4.10.1+ escaping)
+      .replace(/\\\n/g, '\n')
       // Triple-backtick blocks → WhatsApp monospace blocks (same syntax)
       .replace(/```([\s\S]*?)```/g, '```$1```')
       // Italic **first**, but only single‐star or single‐underscore