feat: Adding XIT RIT in the Flex panel

internal/cat/cat.go

@@ -304,6 +304,13 @@ type FlexTXState struct {
 	ANFLevel     int      `json:"anf_level"`
 	WNB          bool     `json:"wnb"`
 	WNBLevel     int      `json:"wnb_level"`
+	// 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.
+	RIT     bool `json:"rit"`
+	RITFreq int  `json:"rit_freq"`
+	XIT     bool `json:"xit"`
+	XITFreq int  `json:"xit_freq"`
 	// CW / mode-specific controls.
 	Mode           string `json:"mode,omitempty"` // active slice mode (CW/USB/LSB/DIGU…)
 	CWSpeed        int    `json:"cw_speed"`
@@ -378,6 +385,10 @@ type FlexController interface {
 	SetAPFLevel(int) error
 	SetWNB(bool) error
 	SetWNBLevel(int) error
+	SetRIT(bool) error
+	SetRITFreq(int) error
+	SetXIT(bool) error
+	SetXITFreq(int) error
 	// CW keyer + mode-specific controls.
 	SetCWSpeed(int) error
 	SetCWPitch(int) error