feat(cases): add case visibility notificaiton

[aaronherman]

This pull request introduces functionality to notify users when the visibility of a case changes. The most important changes include adding a new message type for case visibility updates, updating the notification logic to handle visibility changes, and extending templates to include visibility information.

Notification Enhancements:

• src/dispatch/case/messaging.py: Added CASE_VISIBILITY_CHANGE to the list of message types and updated the send_case_update_notifications function to detect and handle changes in case visibility. This includes appending the new message type to the notification template and passing the old and new visibility values to the notification context.

[Copilot]

Pull Request Overview

This PR adds notifications for when a case’s visibility changes by introducing a new message type and extending the notification logic and templates accordingly.

• Adds CASE_VISIBILITY_CHANGE description and template in strings.py
• Updates send_case_update_notifications to detect visibility changes and include old/new visibility in the context

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/dispatch/messaging/strings.py	Introduce CASE_VISIBILITY_CHANGE_DESCRIPTION and template
src/dispatch/case/messaging.py	Append new message type on visibility change and pass visibility context

Comments suppressed due to low confidence (2)

src/dispatch/case/messaging.py:223

• Add unit tests for visibility change notifications to ensure that when previous_case.visibility differs from case.visibility, the CASE_VISIBILITY_CHANGE message is correctly sent and context variables are populated.

            if previous_case.visibility != case.visibility:

src/dispatch/messaging/strings.py:557

• [nitpick] Consider adding a comment or updating the project documentation to mention the new CASE_VISIBILITY_CHANGE message type so that consumers of the messaging API know about this new notification.

CASE_VISIBILITY_CHANGE_DESCRIPTION = """