feat(tci): the transmit meters, and no temperature invented

TX_POWER and TX_SWR are read-only commands the radio answers when asked,
so they are asked for on each poll of a KEYED radio and not at all
otherwise: a receiving station pays nothing for meters nobody is watching.
Both appear next to the S-meter only while transmitting, because showing
them the rest of the time would show the last thing that happened as if it
were now.

An SWR of 0 draws as '—' rather than as 1.0. A perfect match on an antenna
nobody has measured is the one reading an operator should never be handed.

There is no temperature. The protocol's command list has TX_POWER and
TX_SWR and nothing thermal at all — so rather than leave the question
hanging, it is written down where the next person will look for it. A
temperature invented from something else, on a transmitter, is exactly the
kind of number somebody would trust.

internal/cat/tci_panel.go

@@ -68,6 +68,17 @@ type TCIPanelState struct {
 	// several times a second while receiving.
 	SMeter int `json:"smeter"`
 
+	// TXPowerW and TXSWR are the transmit meters. READ-ONLY in TCI, and only
+	// answered while transmitting — asked for on every poll of a keyed radio,
+	// see ReadState.
+	//
+	// There is no temperature in this protocol. The command list has TX_POWER
+	// and TX_SWR and nothing thermal at all, so a temperature reading here would
+	// have to be invented, and an invented temperature on a transmitter is the
+	// kind of number somebody trusts.
+	TXPowerW float64 `json:"tx_power_w"`
+	TXSWR    float64 `json:"tx_swr"`
+
 	// Modulations is what this radio will accept, straight from its own
 	// announcement, so the mode buttons are the radio's and not a guess.
 	Modulations []string `json:"modulations,omitempty"`
@@ -194,6 +205,14 @@ func (t *TCI) handlePanel(name string, get func(int) string, args string) bool {
 		if forRX0() {
 			p.Lock = yes(get(1))
 		}
+	case "tx_power":
+		if v, err := strconv.ParseFloat(strings.TrimSpace(get(0)), 64); err == nil {
+			p.TXPowerW = v
+		}
+	case "tx_swr":
+		if v, err := strconv.ParseFloat(strings.TrimSpace(get(0)), 64); err == nil {
+			p.TXSWR = v
+		}
 	case "rx_smeter":
 		if n, ok := num(get(1)); ok && forRX0() {
 			p.SMeter = n