feat(udp): spot clicks switch the decoder's mode

Configure (message 15), mode field only, every other field sent as
no-change: an FT4 spot clicked while WSJT-X sits in FT8 lands the operator
ready to decode instead of staring at gibberish. Sent to every instance
heard this session — one already in the right mode treats it as a no-op —
and only for modes the decoder actually speaks (FT8/FT4/JT65/JT9/MSK144/
Q65/FST4); CW and SSB are none of its business. Toggle in the Connections
panel, on by default.

frontend/wailsjs/go/main/App.js

@@ -222,6 +222,10 @@ export function ComputeStationInfo(arg1, arg2) {
   return window['go']['main']['App']['ComputeStationInfo'](arg1, arg2);
 }
 
+export function ConfigureDecoderMode(arg1) {
+  return window['go']['main']['App']['ConfigureDecoderMode'](arg1);
+}
+
 export function ConnectAllClusters() {
   return window['go']['main']['App']['ConnectAllClusters']();
 }
@@ -1178,6 +1182,10 @@ export function GetWorkedCallVariants() {
   return window['go']['main']['App']['GetWorkedCallVariants']();
 }
 
+export function GetWsjtFollowMode() {
+  return window['go']['main']['App']['GetWsjtFollowMode']();
+}
+
 export function GetWsjtHighlight() {
   return window['go']['main']['App']['GetWsjtHighlight']();
 }
@@ -2434,6 +2442,10 @@ export function SetWorkedCallVariants(arg1) {
   return window['go']['main']['App']['SetWorkedCallVariants'](arg1);
 }
 
+export function SetWsjtFollowMode(arg1) {
+  return window['go']['main']['App']['SetWsjtFollowMode'](arg1);
+}
+
 export function SetWsjtHighlight(arg1) {
   return window['go']['main']['App']['SetWsjtHighlight'](arg1);
 }