Update dependency astro to v6 [SECURITY]

Author: renovate[bot]

package.json

@@ -27,7 +27,7 @@
     "@mdx-js/language-server": "~0.6.0",
     "@tailwindcss/vite": "^4.1.8",
     "@types/luxon": "~3.7.0",
-    "astro": "^5.16.0",
+    "astro": "^6.0.0",
     "eslint": "~9.39.0",
     "eslint-plugin-astro": "~1.5.0",
     "prettier": "~3.7.0",