Upgrade ESLint to v9 to fix Vercel deployment

Updated ESLint from 8.57.1 to 9.39.1 to resolve peer dependency conflict with eslint-config-next@16.0.3 which requires ESLint >=9.0.0.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -43,7 +43,7 @@
     "@types/react": "^19.2.5",
     "autoprefixer": "^10.4.22",
     "concurrently": "^9.2.1",
-    "eslint": "^8.57.1",
+    "eslint": "^9.39.1",
     "eslint-config-next": "^16.0.3",
     "postcss": "^8.5.6",
     "tailwindcss": "^3.4.18",