feat: Implement persistence for plant placements in layout editor

backend/prisma/schema.prisma

@@ -644,6 +644,8 @@ model FacilityPlant {
   tagNumber   String   @unique // METRC tag
   batchId     String?
   batch       Batch?   @relation(fields: [batchId], references: [id])
+  plantTypeId String?
+  plantType   PlantType? @relation(fields: [plantTypeId], references: [id])
   position    FacilityPosition @relation(fields: [positionId], references: [id])
   positionId  String   @unique
   address     String   // Full hierarchical address

backend/src/routes/layout.routes.ts

@@ -591,7 +591,7 @@ export async function layoutRoutes(fastify: FastifyInstance, options: FastifyPlu
         handler: async (request, reply) => {
             try {
                 const { id } = request.params as any;
-                const { batchId } = request.body as any;
+                const { batchId, plantTypeId } = request.body as any;
 
                 const position = await prisma.facilityPosition.findUnique({
                     where: { id },
@@ -614,6 +614,7 @@ export async function layoutRoutes(fastify: FastifyInstance, options: FastifyPlu
                         data: {
                             tagNumber: `P-${Date.now()}-${Math.floor(Math.random() * 1000)}`,
                             batchId,
+                            plantTypeId,
                             positionId: id,
                             address,
                             status: 'ACTIVE'

frontend/src/components/layout-editor/LayoutEditor.tsx

@@ -55,15 +55,23 @@ export function LayoutEditor({ floorId, className }: LayoutEditorProps) {
             rows: section.rows,
             columns: section.columns,
             tiers: 1, // TODO: get from section
-            slots: section.positions.map(pos => ({
-                id: pos.id,
-                row: pos.row,
-                column: pos.column,
-                tier: pos.tier,
-                status: pos.status as PlantSlotData['status'],
-                plantType: pos.plant ? plantTypes.find(pt => pt.strain === pos.plant?.strain) : undefined,
-                tagNumber: pos.plant?.tagNumber,
-            })),
+            slots: section.positions.map(pos => {
+                // Find plant type by ID (new way) or strain name (legacy way)
+                const mappedPlantType = pos.plant
+                    ? plantTypes.find(pt => pt.id === pos.plant?.plantTypeId) ||
+                    plantTypes.find(pt => pt.strain === pos.plant?.strain)
+                    : undefined;
+
+                return {
+                    id: pos.id,
+                    row: pos.row,
+                    column: pos.column,
+                    tier: pos.tier,
+                    status: pos.status as PlantSlotData['status'],
+                    plantType: mappedPlantType,
+                    tagNumber: pos.plant?.tagNumber,
+                };
+            }),
         }))
     ) || [];
 
@@ -72,10 +80,17 @@ export function LayoutEditor({ floorId, className }: LayoutEditorProps) {
     }, []);
 
     const handleSlotDrop = useCallback(async (slot: PlantSlotData, plantType: LayoutPlantType) => {
-        console.log('Dropped', plantType.name, 'onto slot', slot.id);
-        // TODO: Implement actual placement via API
-        // For now, just log the action
-    }, []);
+        try {
+            await layoutApi.occupyPosition(slot.id, { plantTypeId: plantType.id });
+
+            // Reload floor data to reflect changes
+            const floor = await layoutApi.getFloor3D(floorId);
+            setFloorData(floor);
+        } catch (e) {
+            console.error('Failed to place plant:', e);
+            setError('Failed to place plant. Please try again.');
+        }
+    }, [floorId]);
 
     const handleDragStart = useCallback((plantType: LayoutPlantType) => {
         setDraggingType(plantType);

frontend/src/lib/layoutApi.ts

@@ -246,8 +246,8 @@ export const layoutApi = {
         return response.data;
     },
 
-    async placeBatchInPosition(positionId: string, batchId: string): Promise<void> {
-        await api.post(`/layout/positions/${positionId}/occupy`, { batchId });
+    async occupyPosition(positionId: string, data: { batchId?: string; plantTypeId?: string }): Promise<void> {
+        await api.post(`/layout/positions/${positionId}/occupy`, data);
     },
 
     async fillSection(sectionId: string, batchId: string, maxCount?: number): Promise<{ plantsCreated: number; message: string }> {