feature: add Create Node action for orphaned node creation

Right-clicking on empty graph area (outside any node or edge) now shows
a context menu with a single 'Create Node' option. Clicking it adds a new
node with a random label and no edges, allowing the user to wire it up
manually afterwards.

- NodeContext gains isEmptyArea flag to distinguish empty-area from node
  right-clicks
- Container div contextmenu handler covers the white space below the SVG;
  SVG-level handler covers empty space within the rendered graph
- node contextmenu handler calls stopPropagation so the SVG handler never
  fires for node clicks; SVG handler also guards via target.closest check
- NodeContextMenu renders emptyAreaItems (Create Node only) vs nodeItems
  (Rename / Subgraph / Remove) based on the flag
- randomWordList extracted as a named export so NodeContextMenu can reuse
  the same word bank
- Three new Playwright e2e tests cover: empty-area menu shows only Create
  Node, created node is orphaned (no new edges), node right-click does not
  show Create Node

src/components/Graph.tsx

@@ -46,6 +46,7 @@ export interface NodeContext {
   nodeId: string;
   nodeName?: string;
   coords: { x: number, y: number };
+  isEmptyArea?: boolean;
 }
 
 export interface GraphContext {
@@ -116,6 +117,22 @@ const Graph = forwardRef<GraphHandle, { setGraphPath: React.Dispatch<React.SetSt
     }
   }, [nodeContext]);
 
+  useEffect(() => {
+    const container = containerRef.current as unknown as HTMLElement;
+    if (!container) return;
+    const handler = (event: MouseEvent) => {
+      if ((event.target as Element).closest('svg')) return;
+      event.preventDefault();
+      openNodeContext({
+        nodeId: '',
+        coords: { x: event.clientX, y: event.clientY },
+        isEmptyArea: true,
+      });
+    };
+    container.addEventListener('contextmenu', handler);
+    return () => container.removeEventListener('contextmenu', handler);
+  }, []);
+
   useEffect(() => {
     if (loadCount === 0) return;
     const state = useGraphsStore.getState() as { graphsById: Map<string, GraphModel> };
@@ -203,12 +220,26 @@ const Graph = forwardRef<GraphHandle, { setGraphPath: React.Dispatch<React.SetSt
         }
 
         event.preventDefault();
+        event.stopPropagation();
         openNodeContext({
           nodeId: id,
           nodeName: node.label,
           coords: { x: event.clientX, y: event.clientY },
         })
       });
+
+    svg.on('contextmenu', function (event) {
+      const target = event.target as Element;
+      if (target.closest('g.node') || target.closest('g.edge')) {
+        return;
+      }
+      event.preventDefault();
+      openNodeContext({
+        nodeId: '',
+        coords: { x: event.clientX, y: event.clientY },
+        isEmptyArea: true,
+      });
+    });
   }
 
   function linkSelectedNodesAsParents(childNodeId: string) {
@@ -222,11 +253,7 @@ const Graph = forwardRef<GraphHandle, { setGraphPath: React.Dispatch<React.SetSt
   }
 
   function getRandomWords(count: number) {
-    const wordList = ['Apple', 'Sun', 'Flame', 'Earth', 'Forest', 'Dream', 'Sky', 'Shadow', 'Flower', 'Ocean', 'River', 'Path', 'Sand', 'Night', 'Star', 'Rain', 'Light', 'Tree', 'Wave', 'Storm', 'Stone', 'Snow', 'Cloud', 'Heart', 'Mountain', 'Leaf', 'Bird', 'Wind', 'Fire', 'Wolf'];
-
-    return wordList
-      .sort(() => Math.random() - 0.5)
-      .slice(0, count);
+    return randomWordList(count);
   }
 
   function createPathSegment(
@@ -281,6 +308,11 @@ const Graph = forwardRef<GraphHandle, { setGraphPath: React.Dispatch<React.SetSt
 
 export default Graph;
 
+export function randomWordList(count: number) {
+  const wordList = ['Apple', 'Sun', 'Flame', 'Earth', 'Forest', 'Dream', 'Sky', 'Shadow', 'Flower', 'Ocean', 'River', 'Path', 'Sand', 'Night', 'Star', 'Rain', 'Light', 'Tree', 'Wave', 'Storm', 'Stone', 'Snow', 'Cloud', 'Heart', 'Mountain', 'Leaf', 'Bird', 'Wind', 'Fire', 'Wolf'];
+  return wordList.sort(() => Math.random() - 0.5).slice(0, count);
+}
+
 export function defaultGraph(): GraphModel {
   const start = crypto.randomUUID();
   const end = crypto.randomUUID();

src/components/NodeContextMenu.tsx

@@ -1,11 +1,11 @@
 import { Dropdown, type MenuProps } from "antd";
-import { defaultGraph, graphContext, GraphModel, type EdgeModel, type NodeContext } from "./Graph";
+import { defaultGraph, graphContext, GraphModel, randomWordList, type EdgeModel, type NodeContext } from "./Graph";
 import { useContext } from "react";
 import { cloneDeep } from "lodash";
 import { useGraphsStore } from "../stores/GraphsStore";
 import { useGraphLayersTreeStore } from "../stores/TreeStore";
 
-const items: MenuProps['items'] = [
+const nodeItems: MenuProps['items'] = [
   {
     key: 'rename',
     label: 'Rename',
@@ -23,6 +23,13 @@ const items: MenuProps['items'] = [
   }
 ]
 
+const emptyAreaItems: MenuProps['items'] = [
+  {
+    key: 'create',
+    label: 'Create Node',
+  }
+]
+
 export default function NodeContextMenu({
   nodeContext,
   contextMenuOpened,
@@ -38,6 +45,7 @@ export default function NodeContextMenu({
     return;
   }
 
+  const items = nodeContext.isEmptyArea ? emptyAreaItems : nodeItems;
   const graphContextValue = useContext(graphContext)!;
   const graphsById = useGraphsStore((s) => (s as { graphsById: Map<string, GraphModel> }).graphsById);
   const addTreeNode = useGraphLayersTreeStore(store => store.add);
@@ -60,6 +68,11 @@ export default function NodeContextMenu({
         removeTreeNode(nodeContext.nodeId);
         break;
       }
+      case 'create': {
+        const id = crypto.randomUUID();
+        graphContextValue.setGraph(prev => ({ ...prev, nodes: [...prev.nodes, { id, label: randomWordList(1)[0] }] }));
+        break;
+      }
       case 'subgraph': {
         graphsById.set(graphContextValue.graphId, cloneDeep(graphContextValue.graph));
         graphContextValue.selectGraphId(nodeContext.nodeId);