feat: add Storybook with component stories

Installs @storybook/nextjs-vite. Stories co-located with components,
grouped by layer (Shared/Entities/Widgets). Multi-variant cases use
render functions instead of one story per variant/size.

src/widgets/Navigation/ui/UtilityBar.stories.tsx

@@ -0,0 +1,20 @@
+import type { Meta, StoryObj } from '@storybook/nextjs-vite'
+import { UtilityBar } from './UtilityBar'
+
+const meta: Meta<typeof UtilityBar> = {
+  title: 'Widgets/UtilityBar',
+  component: UtilityBar,
+  decorators: [
+    (Story) => (
+      <div className="relative h-24 bg-ochre-clay">
+        <Story />
+      </div>
+    ),
+  ],
+}
+
+export default meta
+
+type Story = StoryObj<typeof UtilityBar>
+
+export const Default: Story = {}