Event when there's no milestones - display something in milestones index

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The issue title suggests adding a display for when there are no milestones in the milestones index view. Look for the view function that renders the milestones index, likely in a file like `src/View/Milestones.elm`. Check how the list of milestones is currently rendered and what conditional logic exists. Determine what message or UI element to show when the list is empty, then update the view accordingly.

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