fix: Preserve single newlines in outgoing email messages (#14138)

# Pull Request Template

## Description

This PR fixes an issue where outgoing Email messages (via API) do not
preserve single line breaks in rendered HTML.

#### Cause

Messages are stored with `\n`, but rendering differs:

* **Other channel** (`markdown-it`, `breaks: true`) → `\n` → `<br>`
* **Email** (CommonMark) without `HARDBREAKS` → `\n` collapsed into
spaces

Result: multi-line messages appear as a single paragraph in Email.

#### Solution

* Added `hardbreaks:` option to `render_message` (default: false)
* Enabled `hardbreaks: true` in `EmailHelper#render_email_html`

This ensures `\n` renders as `<br />` in Email, matching web widget
behavior.


Fixes
https://linear.app/chatwoot/issue/CW-6941/outgoing-email-messages-strip-single-newlines-from-plain-text-content

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

#### Screenshots

**Before**
<img width="604" height="104" alt="image"
src="https://github.com/user-attachments/assets/f9086ffb-a5c7-4688-99aa-97ea5edcccde"
/>


**After**
<img width="604" height="210" alt="image"
src="https://github.com/user-attachments/assets/a8f21c76-bcb8-4058-937a-dd185fb6745c"
/>



## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/helpers/email_helper.rb

@@ -7,7 +7,7 @@ module EmailHelper
   def render_email_html(content)
     return '' if content.blank?
 
-    ChatwootMarkdownRenderer.new(content).render_message.to_s
+    ChatwootMarkdownRenderer.new(content).render_message(hardbreaks: true).to_s
   end
 
   # Raise a standard error if any email address is invalid

lib/chatwoot_markdown_renderer.rb

@@ -3,8 +3,8 @@ class ChatwootMarkdownRenderer
     @content = content
   end
 
-  def render_message
-    markdown_renderer = BaseMarkdownRenderer.new
+  def render_message(hardbreaks: false)
+    markdown_renderer = BaseMarkdownRenderer.new(options: hardbreaks ? [:HARDBREAKS] : :DEFAULT)
     doc = CommonMarker.render_doc(@content, :DEFAULT, [:strikethrough, :autolink])
     html = markdown_renderer.render(doc)
     render_as_html_safe(html)