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/kenwood.go

@@ -98,11 +98,11 @@ type Kenwood struct {
 	// Panel state — the K3/K4 control panel, see kenwood_panel.go. Read on the
 	// same serialised link as everything else, on a slow beat for the settings
 	// and every poll for the meters.
-	panel        KenwoodTXState
+	panel KenwoodTXState
 	// The icon/status word, for working out which bit says "ATU in line" — see
 	// probeIcons. Kept so only CHANGES are logged.
-	lastIcons  string
-	iconProbes int
+	lastIcons    string
+	iconProbes   int
 	panelCycle   int
 	panelLoaded  bool
 	metersLogged int