feat(bandopen): a blinking badge that lasts as long as the opening does

The only sign of a detection was a toast. It is gone in seconds, and an operator
who was tuning at that moment had no way back to it — for an event that lasts
hours and happens a handful of times a season, that is the wrong shape entirely.

The badge sits at the right-hand end of the status bar, before the clock: an
opening is a state of the WORLD, not of this station, so it belongs with the
time and the logbook rather than among the rig and amplifier chips.

Knowing when to go out was the real work. Nothing announces that an opening
ended, and the detector deliberately says nothing more about a band for 45
minutes after announcing it — right for a message, useless for a badge. So it is
inferred: every qualifying spot on that band pushes a deadline out, and when
they stop arriving the badge fades by itself. Fifteen minutes, comfortably more
than the detector's own twelve-minute window, so a quiet couple of minutes
mid-opening does not blink it off and on again.

Gated on the same distance floor the detector uses. Without that, a band busy
with short-range tropo would hold an Es badge lit indefinitely on spots the
detector itself had refused.

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

@@ -442,6 +442,8 @@ export function GetIcomState():Promise<cat.IcomTXState>;
 
 export function GetListsSettings():Promise<main.ListsSettings>;
 
+export function GetLiveOpenings():Promise<Array<bandopen.Opening>>;
+
 export function GetLiveStations():Promise<Array<main.LiveStation>>;
 
 export function GetLoTWUsersStatus():Promise<main.LoTWUsersStatus>;

frontend/wailsjs/go/main/App.js

@@ -826,6 +826,10 @@ export function GetListsSettings() {
   return window['go']['main']['App']['GetListsSettings']();
 }
 
+export function GetLiveOpenings() {
+  return window['go']['main']['App']['GetLiveOpenings']();
+}
+
 export function GetLiveStations() {
   return window['go']['main']['App']['GetLiveStations']();
 }