build(deps): bump astro from 5.18.1 to 6.1.5 in /site

Bumps [astro](https://github.com/withastro/astro/tree/HEAD/packages/astro) from 5.18.1 to 6.1.5.
- [Release notes](https://github.com/withastro/astro/releases)
- [Changelog](https://github.com/withastro/astro/blob/main/packages/astro/CHANGELOG.md)
- [Commits](https://github.com/withastro/astro/commits/astro@6.1.5/packages/astro)

---
updated-dependencies:
- dependency-name: astro
  dependency-version: 6.1.5
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

site/package.json

@@ -13,7 +13,7 @@
     "@tailwindcss/vite": "^4.2.2",
     "@iconify-json/lucide": "^1.2.102",
     "@rollup/plugin-yaml": "^4.0.0",
-    "astro": "^5.0.0",
+    "astro": "^6.1.5",
     "astro-icon": "^1.0.0",
     "js-yaml": "^4.1.0",
     "pagefind": "^1.0.0",