feat(tui): click-to-inspect sparkline tooltips in detail view

Click any sparkline character to see data point details — approximate
time, latency, and up/down status. Esc dismisses tooltip without
leaving detail view. Uses existing BubbleZone infrastructure with
zone-relative coordinate math for index resolution.

internal/tui/view_dashboard.go

@@ -95,7 +95,7 @@ func (m Model) View() string {
 		}
 		return ""
 	case stateDetail:
-		return m.viewDetailPanel()
+		return m.zones.Scan(m.viewDetailPanel())
 	case stateHistory:
 		return m.viewHistoryPanel()
 	case stateSLA: