Send a notification when a customer adds comments on line items

As a Salesbuildr user,
I want to receive a notification when a customer adds comments on line items in a proposal,
So that I can promptly respond to their feedback or questions.

Acceptance Criteria:

When a customer adds a comment to a line item in a proposal,
A notification is generated for the Salesbuildr user associated with that proposal.
The notification includes information about which customer added the comment, on which line item, and the content of the comment.
The notification is sent through the user's preferred channel (e.g., email, in-app notification, etc.)

Jira: TN-3652