chore(screener): add @xyflow/react + vitest test environment

src/test-setup.js

@@ -0,0 +1,34 @@
+import '@testing-library/jest-dom/vitest';
+
+// jsdom polyfills for react-flow
+if (typeof window !== 'undefined') {
+  if (!window.matchMedia) {
+    window.matchMedia = (query) => ({
+      matches: false,
+      media: query,
+      onchange: null,
+      addEventListener: () => {},
+      removeEventListener: () => {},
+      addListener: () => {},
+      removeListener: () => {},
+      dispatchEvent: () => false,
+    });
+  }
+  if (!window.ResizeObserver) {
+    window.ResizeObserver = class {
+      observe() {}
+      unobserve() {}
+      disconnect() {}
+    };
+  }
+  if (!window.DOMMatrixReadOnly) {
+    window.DOMMatrixReadOnly = class {
+      constructor() {}
+      m22 = 1;
+    };
+  }
+}
+
+beforeEach(() => {
+  localStorage.clear();
+});