feat: Add rich text support for widget welcome tagline (#11666)

# Pull Request Template

## Description

This PR adds rich text support for the widget welcome tagline, enabling
users to format the message using basic text styling (bold, italics,
links, etc.)
https://github.com/chatwoot/chatwoot/pull/11629#issuecomment-2932448975

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

### Screenshots
<img width="1100" alt="image"
src="https://github.com/user-attachments/assets/eef2bfd3-7bc9-4aea-b21d-078f6b29f334"
/>
<img width="448" alt="image"
src="https://github.com/user-attachments/assets/713c6b07-d0dc-4c8f-bfba-cd119a858375"
/>



## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [ ] 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
- [ ] 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/views/widgets/show.html.erb

@@ -11,7 +11,7 @@
         locale: '<%= @web_widget.account.locale %>',
         websiteName: '<%= @web_widget.inbox.name %>',
         websiteToken: '<%= @web_widget.website_token %>',
-        welcomeTagline: '<%= @web_widget.welcome_tagline %>',
+        welcomeTagline: <%= @web_widget.welcome_tagline.to_json.html_safe %>,
         welcomeTitle: '<%= @web_widget.welcome_title %>',
         widgetColor: '<%= @web_widget.widget_color %>',
         portal: <%= @web_widget.inbox.portal.to_json.html_safe %>,