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/entities/experience/ui/ExperienceCard.stories.tsx

@@ -0,0 +1,40 @@
+import type { Meta, StoryObj } from '@storybook/nextjs-vite'
+import { ExperienceCard } from './ExperienceCard'
+
+const meta: Meta<typeof ExperienceCard> = {
+  title: 'Entities/ExperienceCard',
+  component: ExperienceCard,
+  decorators: [
+    (Story) => (
+      <div className="p-8 bg-white max-w-2xl">
+        <Story />
+      </div>
+    ),
+  ],
+}
+
+export default meta
+
+type Story = StoryObj<typeof ExperienceCard>
+
+const baseArgs = {
+  title: 'Senior Frontend Engineer',
+  company: 'Acme Corp',
+  period: '2021 – 2024',
+  description: 'Led frontend development for the core product, established design system practices, and mentored junior engineers across two distributed teams.',
+}
+
+export const Default: Story = {
+  args: baseArgs,
+}
+
+export const SlateBackground: Story = {
+  render: () => (
+    <div className="bg-slate-indigo p-8 max-w-2xl">
+      <ExperienceCard
+        {...baseArgs}
+        className="border-ochre-clay"
+      />
+    </div>
+  ),
+}