feat: add new features including SEO, sitemap, and subjects management

- Create robots.txt to allow search engine indexing and specify sitemap location.
- Implement ajouterSujet.js for adding new subjects to sujets.json.
- Develop dynamic subject pages in page.tsx using static generation with metadata.
- Add contact, error, not found, and privacy policy pages for improved user experience.
- Generate sitemap.xml for better search engine visibility.
- Create SEO component for managing page metadata.
- Populate sujets.json with detailed subject information for dynamic content rendering.

package.json

@@ -11,7 +11,9 @@
   "dependencies": {
     "next": "16.1.6",
     "react": "19.2.3",
-    "react-dom": "19.2.3"
+    "react-dom": "19.2.3",
+    "react-markdown": "^10.1.0",
+    "ts-node": "^10.9.2"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
@@ -21,6 +23,6 @@
     "eslint": "^9",
     "eslint-config-next": "16.1.6",
     "tailwindcss": "^4",
-    "typescript": "^5"
+    "typescript": "^5.9.3"
   }
 }