fix: Flex with multiple slices opened was always showing slice A s-meter.

internal/cat/cat.go

@@ -330,6 +330,7 @@ type FlexMeter struct {
 	Src   string  `json:"src,omitempty"`  // SLC / TX- / RAD / AMP…
 	Name  string  `json:"name,omitempty"` // FWDPWR, SWR, LEVEL, PATEMP…
 	Unit  string  `json:"unit,omitempty"`
+	Slice int     `json:"slice"`          // for SLC meters, the slice index it belongs to; -1 otherwise
 	Value float64 `json:"value"`
 	Lo    float64 `json:"lo"`
 	Hi    float64 `json:"hi"`