fix: the Flex panel DAX button now toggles the TRANSMIT-bar DAX (transmit set dax=), not the slice RX DAX channel — this is the button that routes TX audio through DAX (WSJT-X); state follows changes made in SmartSDR too

internal/cat/cat.go

@@ -319,6 +319,7 @@ type FlexTXState struct {
 	NRFLevel     int  `json:"nrf_level"`
 	DSPV4        bool `json:"dsp_v4"`
 	DAXCh        int  `json:"dax_ch"` // DAX audio channel of the active slice (0 = off, 1-8)
+	TXDAX        bool `json:"tx_dax"` // DAX is the TX audio source (SmartSDR transmit-bar DAX button)
 	// RIT/XIT — offsets applied to the active slice's RX / TX frequency without
 	// moving the slice. The offset survives the switch being turned off, so
 	// re-enabling restores it, exactly like the radio's own knob.
@@ -412,7 +413,8 @@ type FlexController interface {
 	SetANFT(bool) error
 	SetNRF(bool) error
 	SetNRFLevel(int) error
-	SetDAX(int) error // DAX channel 0 (off) - 8
+	SetDAX(int) error    // slice RX DAX channel 0 (off) - 8
+	SetTXDAX(bool) error // TX audio from DAX (transmit set dax=)
 	SetRIT(bool) error
 	SetRITFreq(int) error
 	SetXIT(bool) error