perf: guard setHoveredNodeId against redundant store mutations

Skip Zustand set() when hoveredNodeId already matches the incoming value.
Prevents redundant store updates when the mouse stays on the same node
or when onMouseLeave fires with null when already null.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/store/workflowStore.ts

@@ -526,7 +526,7 @@ const workflowStoreImpl: StateCreator<WorkflowStore> = (set, get) => ({
   },
 
   setHoveredNodeId: (id: string | null) => {
-    set({ hoveredNodeId: id });
+    if (get().hoveredNodeId !== id) set({ hoveredNodeId: id });
   },
 
   addNode: (type: NodeType, position: XYPosition, initialData?: Partial<WorkflowNodeData>) => {