feat(dvk): delete a message — recording and label together

A deleted message is a free slot, per its operator; keeping the label made it
look half-deleted.

app.go

@@ -10300,6 +10300,22 @@ func (a *App) GetDVKMessages() []DVKMessage {
 	return out
 }
 
+// DVKDelete removes a slot's recording AND its label — a deleted message is a
+// free slot, per its operator.
+func (a *App) DVKDelete(slot int) error {
+	if slot < 1 || slot > dvkSlots {
+		return fmt.Errorf("bad slot")
+	}
+	if err := os.Remove(a.dvkPath(slot)); err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("delete message %d: %w", slot, err)
+	}
+	if a.settings != nil {
+		_ = a.settings.Set(a.ctx, dvkLabelKey(slot), "")
+	}
+	applog.Printf("dvk: message F%d deleted (label cleared)", slot)
+	return nil
+}
+
 // SetDVKLabel renames a voice-keyer slot.
 func (a *App) SetDVKLabel(slot int, label string) error {
 	if a.settings == nil {