feat: report UI crashes instead of showing a blank window

Two white-screen reports are open — one after logging a 10 GHz QSO, one on
starting a DVK auto-call — and neither could be investigated, for the same
reason: a render error emptied the window and left NOTHING. No line in
opslog.log, no dialog, nothing the operator could send but the words "white
screen". A fault the user cannot report is a fault that cannot be fixed.

So before hunting either trigger, the reporting path:

  - An error boundary catches a render throw, writes the error and component
    stack to the app log through the new LogUIError binding, and shows it on
    screen — selectable, with Copy and Reload.
  - Global handlers catch what a boundary cannot: throws from timers, event
    handlers and rejected promises. An auto-call loop lives entirely in
    callbacks, which is exactly where the second report came from, and those
    leave no trace at all today.

It deliberately does not try to resume: React cannot promise sane state after a
render throw, and a half-working logger would be worse than a clear stop.

This does not fix either crash. It makes the next occurrence arrive with its
cause attached, which is the step that has been missing.

app.go

@@ -1267,6 +1267,27 @@ type StartupStatus struct {
 
 // GetStartupStatus exposes whatever happened during startup so the UI
 // can show a useful error instead of just "db not initialized".
+// LogUIError records a crash or unhandled error from the interface in the app
+// log, with whatever context the window can give.
+//
+// Until this existed, a render error emptied the window and left NOTHING: no
+// line in opslog.log, no dialog. Two separate white-screen reports — one after
+// logging a 10 GHz QSO, one on starting an auto-call — could not be diagnosed at
+// all, because the only evidence lived in a console the operator had to know to
+// open. A fault the user cannot report is a fault that cannot be fixed.
+func (a *App) LogUIError(kind, message, stack string) {
+	msg := strings.TrimSpace(message)
+	if msg == "" {
+		msg = "(no message)"
+	}
+	applog.Printf("ui %s: %s", strings.TrimSpace(kind), msg)
+	if st := strings.TrimSpace(stack); st != "" {
+		// The stack goes in whole: minified frames are still the difference between
+		// "somewhere in the app" and one component.
+		applog.Printf("ui stack: %s", st)
+	}
+}
+
 func (a *App) GetStartupStatus() StartupStatus {
 	return StartupStatus{
 		OK:     a.startupErr == "",