Create banner to indicate system downtime messages

User Story:
When maintenance is required on production, a system alert message should be posted for all users on both the front end and admin interfaces.

We need to notify users so they may expect wonkiness if they choose to use the software at that time.

The issue names no files, tests, or entry points. Start by locating the front-end and admin interface entry points, then determine how a production maintenance message could reach all users in both interfaces. Done means both interfaces display a system downtime banner, though the issue does not specify its wording, trigger, or dismissal behavior.

Written by the indexing model from the issue text.