perf: replace bare useWorkflowStore() calls with selective subscriptions

WorkflowCanvas, Header, and FloatingActionBar all used
useWorkflowStore() without selectors, subscribing to the entire store.
Every hoveredNodeId change triggered re-renders in all three components
plus a full cascade through edges and nodes from WorkflowCanvas.

- WorkflowCanvas: split into individual selectors for clipboard state
- Header: wrap in useShallow with explicit field selection
- FloatingActionBar: wrap in useShallow with explicit field selection

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

src/components/FloatingActionBar.tsx

@@ -2,6 +2,7 @@
 
 import { useRef, useState, useEffect, useMemo, useCallback } from "react";
 import { useWorkflowStore } from "@/store/workflowStore";
+import { useShallow } from "zustand/shallow";
 import { NodeType } from "@/types";
 import { useReactFlow } from "@xyflow/react";
 import { ModelSearchDialog } from "./modals/ModelSearchDialog";
@@ -320,7 +321,21 @@ export function FloatingActionBar() {
     setModelSearchOpen,
     modelSearchOpen,
     modelSearchProvider,
-  } = useWorkflowStore();
+  } = useWorkflowStore(useShallow((state) => ({
+    nodes: state.nodes,
+    isRunning: state.isRunning,
+    currentNodeIds: state.currentNodeIds,
+    executeWorkflow: state.executeWorkflow,
+    regenerateNode: state.regenerateNode,
+    executeSelectedNodes: state.executeSelectedNodes,
+    stopWorkflow: state.stopWorkflow,
+    validateWorkflow: state.validateWorkflow,
+    edgeStyle: state.edgeStyle,
+    setEdgeStyle: state.setEdgeStyle,
+    setModelSearchOpen: state.setModelSearchOpen,
+    modelSearchOpen: state.modelSearchOpen,
+    modelSearchProvider: state.modelSearchProvider,
+  })));
 
   // Get display text for running nodes
   const runningNodeCount = currentNodeIds.length;

src/components/Header.tsx

@@ -2,6 +2,7 @@
 
 import { useState, useRef, useMemo, useCallback } from "react";
 import { useWorkflowStore, WorkflowFile } from "@/store/workflowStore";
+import { useShallow } from "zustand/shallow";
 import { ProjectSetupModal } from "./ProjectSetupModal";
 import { CostIndicator } from "./CostIndicator";
 import { KeyboardShortcutsDialog } from "./KeyboardShortcutsDialog";
@@ -73,7 +74,22 @@ export function Header() {
     shortcutsDialogOpen,
     setShortcutsDialogOpen,
     setShowQuickstart,
-  } = useWorkflowStore();
+  } = useWorkflowStore(useShallow((state) => ({
+    workflowName: state.workflowName,
+    workflowId: state.workflowId,
+    saveDirectoryPath: state.saveDirectoryPath,
+    hasUnsavedChanges: state.hasUnsavedChanges,
+    lastSavedAt: state.lastSavedAt,
+    isSaving: state.isSaving,
+    setWorkflowMetadata: state.setWorkflowMetadata,
+    saveToFile: state.saveToFile,
+    loadWorkflow: state.loadWorkflow,
+    previousWorkflowSnapshot: state.previousWorkflowSnapshot,
+    revertToSnapshot: state.revertToSnapshot,
+    shortcutsDialogOpen: state.shortcutsDialogOpen,
+    setShortcutsDialogOpen: state.setShortcutsDialogOpen,
+    setShowQuickstart: state.setShowQuickstart,
+  })));
 
   const [showProjectModal, setShowProjectModal] = useState(false);
   const [projectModalMode, setProjectModalMode] = useState<"new" | "settings">("new");

src/components/WorkflowCanvas.tsx

@@ -1283,7 +1283,10 @@ export function WorkflowCanvas() {
   }, []);
 
   // Get copy/paste functions and clipboard from store
-  const { copySelectedNodes, pasteNodes, clearClipboard, clipboard } = useWorkflowStore();
+  const copySelectedNodes = useWorkflowStore((state) => state.copySelectedNodes);
+  const pasteNodes = useWorkflowStore((state) => state.pasteNodes);
+  const clearClipboard = useWorkflowStore((state) => state.clearClipboard);
+  const clipboard = useWorkflowStore((state) => state.clipboard);
 
   // Add non-passive wheel listener to handle zoom/pan and prevent browser navigation
   // This replaces the onWheel prop which is passive by default and can't preventDefault