Include warnings in the alerter, for history tracking

This isn't critical, but it would be nice if the alert bar included a history of the warnings that have come up, so when a warning pop-up appears it'd be nice if it also logs a relevant message to the alerter in the top bar.

Start by locating the alert bar and the warning pop-up components in the TypeScript/Vue application, then trace how warnings are currently raised and displayed. Define the history behavior and message contents with maintainers; done means warnings appear in the top-bar alerter with relevant history entries.

Written by the indexing model from the issue text.