feat(layout): Update frontend types and API to support Tiers

- Added 'tiers' to LayoutSection
- Added 'tier' to LayoutPosition
- Included 'sections' in saveFloorLayout payload (fixes data loss bug)

frontend/src/lib/layoutApi.ts

@@ -50,6 +50,7 @@ export interface LayoutPosition {
     sectionId: string;
     row: number;
     column: number;
+    tier: number;
     slot: number;
     status: string;
     plantId?: string;
@@ -68,6 +69,7 @@ export interface LayoutSection {
     height: number;
     rows: number;
     columns: number;
+    tiers: number;
     spacing?: number;
     positions?: LayoutPosition[];
 }
@@ -124,7 +126,8 @@ export const layoutApi = {
             width: r.width,
             height: r.height,
             color: r.color,
-            rotation: r.rotation
+            rotation: r.rotation,
+            sections: r.sections // Include sections in save
         }));
         const response = await api.post(`/api/layout/floors/${floorId}/layout`, { rooms: roomsForApi });
         return response.data;