place the selection panel beside what it describes

src/lib/eventsystem/event/FloatingLayoutInvalidatedEvent.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include "Event.h"
+
+// Asks the owner of the widgets floating over the game world view to re-run its placement
+// pass (see ui/FloatingPanel.h). Published by a floating widget whose content or
+// visibility changed: what space that widget may take depends on the ones placed before
+// it, so it cannot re-place itself alone (REQ-UI-BUILD-BAR, REQ-UI-CONTROLS-PANEL,
+// REQ-UI-SELECTION-PANEL). Carries no payload -- the pass re-reads every widget.
+class FloatingLayoutInvalidatedEvent : public Event
+{
+};