fix(sat,decodes): the left column holds position too, and drift stops lying

Two things.

The sky plot and the position share the left column now, and the button
that opens it says so the way the right one does — it was a radar icon,
left over from when it toggled a plot inside the readout column, and the
gesture is the same one on both sides. The plot and the numbers are the
same answer at two precisions: azimuth and elevation drawn, then written
out to the digit. Having them at opposite ends of the window meant
reading a bearing off one side and finding it on the other.

And the band-drift warning, reported by W4TE. It compared the decoder's
announced band against RigState.Band, which is the TRANSMIT band — so
with slice A on 20 m running its own WSJT-X, slice B on 40 m, and
transmit focus on B, the 20 m decoder was told the rig was on 40 m while
the slice it listens to had been on 20 m throughout. The panel's own
comment had accepted this as a line that setup could read past; it is
worse than that, because the warning names a band and asserts something
false about the radio.

RigState now carries RxBands: every band the rig has a receiver on. One
entry on a single-VFO rig, one per slice on a Flex, the transmit band
always included so it cannot come back empty while the rig is on a
frequency. The warning fires only when the decoder announces a band
NOTHING on the radio is on, which is what it was always for and what a
lost CAT link actually looks like.

internal/cat/rxbands_test.go

@@ -0,0 +1,66 @@
+package cat
+
+import (
+	"strings"
+	"testing"
+)
+
+// RxBands is what stops the decode panel's band-drift warning from lying to a
+// station running two slices.
+//
+// Reported for W4TE: slice A on 20 m with its own WSJT-X, slice B on 40 m
+// holding transmit focus. RigState.Band is the TRANSMIT band, so the 20 m
+// decoder was told "the rig is on 40M" while the slice it listens to had been
+// on 20 m the whole time.
+func TestRxBandsAlwaysCarriesTheTransmitBand(t *testing.T) {
+	m := &Manager{}
+	got := m.rxBands(RigState{FreqHz: 14074000, Band: "20m"})
+	if len(got) != 1 || got[0] != "20m" {
+		t.Fatalf("got %v, want [20m]", got)
+	}
+}
+
+// A split rig receives on one band and transmits on another — cross-band split
+// is unusual but legal, and the receive side is where a decoder listens.
+func TestRxBandsIncludesTheSplitReceiveBand(t *testing.T) {
+	m := &Manager{}
+	got := m.rxBands(RigState{FreqHz: 14074000, Band: "20m", RxFreqHz: 7074000, Split: true})
+	if !has(got, "20m") || !has(got, "40m") {
+		t.Fatalf("got %v, want both 20m and 40m", got)
+	}
+}
+
+// Nothing to report when the rig is on no frequency: an empty list means "there
+// is nothing to compare with", and the panel treats it as such rather than as
+// "the radio is on no band", which would warn about every decode.
+func TestRxBandsIsEmptyWithNoFrequency(t *testing.T) {
+	m := &Manager{}
+	if got := m.rxBands(RigState{}); len(got) != 0 {
+		t.Fatalf("got %v, want nothing", got)
+	}
+}
+
+// Deduplicated and lower-cased, because the panel compares strings: two slices
+// on the same band are one band, and "20M" from a backend must match "20m" from
+// BandFromHz.
+func TestRxBandsIsNormalised(t *testing.T) {
+	m := &Manager{}
+	got := m.rxBands(RigState{FreqHz: 14074000, Band: "20M", RxFreqHz: 14080000})
+	if len(got) != 1 || got[0] != "20m" {
+		t.Fatalf("got %v, want [20m]", got)
+	}
+	for _, b := range got {
+		if b != strings.ToLower(b) {
+			t.Errorf("%q is not lower-cased", b)
+		}
+	}
+}
+
+func has(list []string, want string) bool {
+	for _, s := range list {
+		if s == want {
+			return true
+		}
+	}
+	return false
+}