fix(sat): both antennas on both satellite slices

A slice has an rxant and a txant, and each pair belongs to that slice's
own band. Only two of the four were being set — the downlink's receive
antenna and the uplink's transmit one — so the downlink slice was left
with an empty txant. It never keys, so nothing was wrong on the air, but
the slice was half-configured: move transmit focus to it and the radio
uses whatever antenna it happened to be left on. Reported with XVTA on
2 m and XVTB on 70 cm, where the 70 cm slice showed one antenna and the
2 m slice showed two.

SatAntennas now takes all four, and the late-slice replay in
adoptSatSlice hands the uplink its own pair instead of putting the
transmit antenna on both of its ports.

internal/cat/cat.go

@@ -594,9 +594,9 @@ type FlexController interface {
 	SetMute(bool) error
 	SetRXAntenna(string) error
 	SetTXAntenna(string) error
-	// SatAntennas sets the antenna on each SATELLITE slice — they are on two
+	// SatAntennas sets BOTH antennas on each SATELLITE slice — they are on two
 	// different bands and, with transverters, two different ports.
-	SatAntennas(rxAnt, txAnt string) error
+	SatAntennas(downRX, downTX, upRX, upTX string) error
 	// SatTone sets the CTCSS tone the satellite uplink transmits (0 = off).
 	SatTone(hz float64) error
 	SetActiveSlice(int) error // focus slice idx so commands target it