feat(k3): a mode row on the Elecraft console — CW/USB/LSB/DATA/DATA-RTTY

The report: switching the K3 to a data mode 'does not work for FT8 — the K3
does not go into DATA'. The mode digit is only half the answer on that radio:
MD6 keeps whatever DT submode the previous session left, and with FSK D still
armed the rig keys FT8 with no rear-audio modulation.

The panel buttons say the whole thing: DATA is MD6+DT0 (DATA A, the soundcard
path), DATA RTTY is MD6+DT2 (FSK D). The DT submode is also read on the
settings beat — Elecraft only, a plain Kenwood would '?;' it — so the active
DATA button follows what the rig is actually in, front-panel changes included.
A dedicated SetKenwoodPanelMode rather than the logger's SetMode: a panel
button is the operator saying exactly what the rig should do, not an ADIF mode
to be mapped through preferences.

frontend/wailsjs/go/models.ts

@@ -1072,6 +1072,7 @@ export namespace cat {
 	    model?: string;
 	    elecraft: boolean;
 	    mode?: string;
+	    data_sub?: string;
 	    transmitting: boolean;
 	    split: boolean;
 	    split_tx_hz: number;
@@ -1108,6 +1109,7 @@ export namespace cat {
 	        this.model = source["model"];
 	        this.elecraft = source["elecraft"];
 	        this.mode = source["mode"];
+	        this.data_sub = source["data_sub"];
 	        this.transmitting = source["transmitting"];
 	        this.split = source["split"];
 	        this.split_tx_hz = source["split_tx_hz"];