fix: clear camera zoom state on camera group switch

In-memory cameraZoomStates was not reset when switching groups,
causing hydration to skip cameras already in state and keep
zoom from the previous group. Resetting on group change lets
hydration reload correct per-group zoom from localStorage.

https://claude.ai/code/session_01WidMYGkyBCFf4L9PnFEiZ5

web/src/views/live/DraggableGridLayout.tsx

@@ -170,6 +170,7 @@ export default function DraggableGridLayout({
     setCurrentCameras(undefined);
     setCurrentIncludeBirdseye(undefined);
     setCurrentGridLayout(undefined);
+    setCameraZoomStates({});
   }, [cameraGroup, setIsEditMode]);
 
   // camera state