🤖 fix(test-runner): avoid redundant theme writes/events to reduce test flakiness

Author: ammar-agent

.storybook/preview.tsx

@@ -19,8 +19,14 @@ const applyStorybookTheme = (mode: ThemeMode) => {
 
   try {
     const serialized = JSON.stringify(mode);
-    window.localStorage.setItem(UI_THEME_KEY, serialized);
+    const prev = window.localStorage.getItem(UI_THEME_KEY);
     const root = document.documentElement;
+    const current = root?.dataset?.theme as ThemeMode | undefined;
+    if (prev === serialized && current === mode) {
+      return; // no-op if already applied
+    }
+
+    window.localStorage.setItem(UI_THEME_KEY, serialized);
     root.dataset.theme = mode;
     root.style.colorScheme = mode;