Store generated HTML content in message database record

[ibsule]

Summary

Store the generated HTML content that will be sent to the user in the database, instead of just the message plain text.

Details

• Update the message entity to include a field for HTML content
• Generate the HTML representation of the message at creation time
• Save both the textual and HTML versions in the database
• Ensure the sending logic uses the correct format as needed

Motivation

Storing the HTML enables better formatting, auditing, and reliability for message delivery.