fix(tci): pick the sideband from the frequency just commanded

Clicking a spot sets the frequency, then the mode 150 ms later, and SetMode
chose USB or LSB from t.freqA — the frequency the radio had ECHOED. From 7 MHz
onto a 14 MHz spot that echo has often not landed, so the sideband was computed
for the band being left: LSB on 20 m. Clicking the same spot again, the echo
having arrived, gave USB. Reported from a SunSDR as 'the frequency is right, the
mode is wrong until I click twice'.

SetFrequency now records what was asked for and SetMode prefers it until the
radio's own echo confirms the move.

The server's 'protocol:' announcement is also kept instead of being filed under
unhandled: it names the ExpertSDR and its TCI version, and panorama spots need
TCI 1.5 — older servers accept the spot commands and silently drop them, which
is indistinguishable from a broken logger. Now it says so.

internal/cat/tci_test.go

@@ -0,0 +1,24 @@
+package cat
+
+import "testing"
+
+func TestTCISpotsUnsupported(t *testing.T) {
+	// SPOT arrived in TCI 1.5. The SunSDR2 PRO report that prompted this was an
+	// ExpertSDR announcing 1.3 — spots accepted and silently dropped.
+	for _, c := range []struct {
+		version string
+		old     bool
+	}{
+		{"1.3", true},
+		{"1.4", true},
+		{"1.5", false},
+		{"1.9", false},
+		{"2.0", false},
+		{"", false},      // unparseable → assume it works
+		{"weird", false}, // refusing to draw on a doubt is the worse mistake
+	} {
+		if got := tciSpotsUnsupported(c.version); got != c.old {
+			t.Errorf("tciSpotsUnsupported(%q) = %v, want %v", c.version, got, c.old)
+		}
+	}
+}