Add EmptyState

Sub-components: EmptyState.IconTile (Phosphor icon in a tinted circle), EmptyState.Illustration (SpotIllustration or custom hero), EmptyState.Title (size-scaled, heading level overridable via render), EmptyState.Description, and EmptyState.Actions. Size flows through context, so each slot scales itself; the recommended media pairing is sm→IconTile, md→SpotIllustration, lg→hero. The root takes an optional intent prop (no default — omit to inherit the palette from an ancestor), so the IconTile and Buttons inside share one colour context. Available from the barrel and the @oztix/roadie-components/empty-state subpath.