fix(tci): send the sensor subscription in both cases

Two rounds of fixes and the SunSDR's meters are still silent. The one remaining
difference from the protocol document is the case: its examples read
TX_SENSORS_ENABLE:true,200; and ours went out lower-case. Every other command
works lower-case, but nothing proves this newer path does — a case-insensitive
server ignores the duplicate, a sensitive one finally hears it.

internal/cat/tci.go

@@ -466,9 +466,16 @@ func (t *TCI) SetTXAudioSource(src string) {
 // "ready", because a subscription sent during the server's initial dump can be
 // dropped. 200 ms is the rate the protocol's own examples use.
 func (t *TCI) subscribeSensors(when string) {
+	// Both cases, deliberately. Every other command this backend sends works in
+	// lower case, but the meters stayed silent on a real SunSDR through two
+	// rounds of fixes — and the protocol document's own examples are upper case
+	// (TX_SENSORS_ENABLE:true,200;). A server that is case-insensitive ignores
+	// the duplicate; one that is not finally hears the subscription.
 	e1 := t.send("rx_sensors_enable:true,200;")
 	e2 := t.send("tx_sensors_enable:true,200;")
-	debugLog.Printf("TCI: sensor subscription sent (%s): rx=%v tx=%v", when, e1, e2)
+	_ = t.send("RX_SENSORS_ENABLE:true,200;")
+	_ = t.send("TX_SENSORS_ENABLE:true,200;")
+	debugLog.Printf("TCI: sensor subscription sent (%s, both cases): rx=%v tx=%v", when, e1, e2)
 }
 
 func (t *TCI) send(cmd string) error {