Warn users deleting scheduler events

Pop up a modal warning users that the scheduler does not backfill without a manually triggered "Populate" action when deleting an event with a schedule id.

Start by locating the scheduler event deletion flow and the UI code that handles events with a schedule id. Confirm how the existing "Populate" action is exposed, then verify that deletion shows a warning explaining that backfill requires manually triggering "Populate".

Written by the indexing model from the issue text.