feat: DAX selector on the Flex panel — routes the active slice's RX audio to a DAX channel (slice dax=0-8, Off..8 dropdown next to the antenna selection, highlighted when active); changelog updated

internal/cat/cat.go

@@ -318,6 +318,7 @@ type FlexTXState struct {
 	NRF          bool `json:"nrf"`
 	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)
 	// 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.
@@ -411,6 +412,7 @@ type FlexController interface {
 	SetANFT(bool) error
 	SetNRF(bool) error
 	SetNRFLevel(int) error
+	SetDAX(int) error // DAX channel 0 (off) - 8
 	SetRIT(bool) error
 	SetRITFreq(int) error
 	SetXIT(bool) error