fix(deps): update dependency astro to v6

Author: renovate[bot]

package.json

@@ -28,7 +28,7 @@
     "@astrojs/starlight": "0.37.7",
     "@astrojs/starlight-tailwind": "4.0.2",
     "@tailwindcss/vite": "4.2.4",
-    "astro": "5.18.1",
+    "astro": "6.3.0",
     "starlight-links-validator": "0.19.2",
     "starlight-scroll-to-top": "0.4.0",
     "tailwindcss": "4.2.4",