fix(bank_panel): repaint footer mode toggle when Design/Arrange action fires

src/bank_panel.h

@@ -117,6 +117,12 @@ void bankPanelToggledPoolFullHeight();
 // Bound to the "banks full-height" action. Requests a repaint.
 void bankPanelToggledBanksFullHeight();
 
+// Requests an immediate repaint of the panel if it is open. A no-op when the panel
+// is closed (safe to call unconditionally). Called by the actions layer after a
+// mode change so the footer [Arrange|Design] toggle reflects the new mode without
+// requiring a hide/reshow.
+void bankPanelInvalidate();
+
 // Tears the panel down on extension unload: destroys the window and releases any
 // cached thumbnails / PCM handles. Mirror of bankPanelInit; safe if never opened.
 void bankPanelShutdown();