fix: 修正 logo 中 N 和 G 字母造型

N 添加对角线笔画（█▄ █），G 添加内横杠（█ ▀█），
避免与 O 字母造型雷同。同步更新 ui.ts 中的硬编码 wordmark。

packages/storybook/.storybook/theme-tool.ts

@@ -0,0 +1,21 @@
+import { createElement } from "react"
+import { useGlobals } from "storybook/manager-api"
+import { ToggleButton } from "storybook/internal/components"
+
+export function ThemeTool() {
+  const [globals, updateGlobals] = useGlobals()
+  const mode = globals.theme === "dark" ? "dark" : "light"
+  const toggle = () => {
+    const next = mode === "dark" ? "light" : "dark"
+    updateGlobals({ theme: next })
+  }
+  return createElement(
+    ToggleButton,
+    {
+      title: "Toggle theme",
+      active: mode === "dark",
+      onClick: toggle,
+    },
+    mode === "dark" ? "Dark" : "Light",
+  )
+}