fix(elecraft): the ATU is switch 19, not 20

SWT20 was written from memory of the reference rather than from Table 7,
and 20 is not an ATU switch at all — it would have pressed something else
on a real K3. An operator read the table out for us: switch 19 is the ATU
row, TAP for a tuning cycle and HOLD for tuner in line or bypassed.

Adds the HOLD as its own ATU button, because on the radio they are two
different things: tuning is a cycle you start, bypassing is a state you
leave it in.

Power takes 0-110 W on an Elecraft, per the reference — a K3 makes a
little over its rated output — while a Kenwood keeps 200.

frontend/wailsjs/go/main/App.d.ts

@@ -1247,6 +1247,8 @@ export function TestUltrabeam(arg1:main.UltrabeamSettings):Promise<void>;
 
 export function TestWebPublishFTP(arg1:webpub.Config):Promise<string>;
 
+export function ToggleKenwoodATU():Promise<void>;
+
 export function TuneKenwoodATU():Promise<void>;
 
 export function TuneYaesuATU():Promise<void>;