feat: migrate docs to Fumadocs framework

- Auto-generated sidebar from file structure
- Built-in search and TOC
- MDX native support with frontmatter
- Removed hand-written Sidebar component
- Docs now at /docs/* route (Landing/Blocks/Create/Examples unchanged)
- Content in content/docs/ as MDX files

packages/docs/package.json

@@ -15,13 +15,17 @@
     "@mdx-js/react": "^3.1.1",
     "@next/mdx": "^16.2.6",
     "@types/mdx": "^2.0.13",
+    "fumadocs-core": "14.7.7",
+    "fumadocs-mdx": "10.1.0",
+    "fumadocs-ui": "14.7.7",
+    "newspaperui": "workspace:*",
+    "newspaperui-theme": "workspace:*",
     "next": "^15.1.6",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "rehype-pretty-code": "^0.14.3",
     "shiki": "^4.1.0",
-    "newspaperui": "workspace:*",
-    "newspaperui-theme": "workspace:*"
+    "zod": "3"
   },
   "devDependencies": {
     "@types/node": "^22.10.5",