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.

package.json

@@ -8,7 +8,9 @@
     "start": "next start",
     "lint": "eslint",
     "test": "vitest run",
-    "test:watch": "vitest"
+    "test:watch": "vitest",
+    "storybook": "storybook dev -p 6006",
+    "build-storybook": "storybook build"
   },
   "dependencies": {
     "clsx": "^2.1.1",
@@ -18,6 +20,11 @@
     "tailwind-merge": "^3.5.0"
   },
   "devDependencies": {
+    "@chromatic-com/storybook": "^5.1.2",
+    "@storybook/addon-a11y": "^10.3.5",
+    "@storybook/addon-docs": "^10.3.5",
+    "@storybook/addon-vitest": "^10.3.5",
+    "@storybook/nextjs-vite": "^10.3.5",
     "@tailwindcss/postcss": "^4",
     "@testing-library/dom": "^10.4.1",
     "@testing-library/jest-dom": "^6.9.1",
@@ -27,9 +34,14 @@
     "@types/react": "^19",
     "@types/react-dom": "^19",
     "@vitejs/plugin-react": "^6.0.1",
+    "@vitest/browser-playwright": "4.1.4",
+    "@vitest/coverage-v8": "4.1.4",
     "eslint": "^9",
     "eslint-config-next": "16.2.4",
+    "eslint-plugin-storybook": "^10.3.5",
     "jsdom": "^29.0.2",
+    "playwright": "^1.59.1",
+    "storybook": "^10.3.5",
     "tailwindcss": "^4",
     "typescript": "^5",
     "vite": "^8.0.8",