fix(site): fix root path resolution for Astro 6 prerendering

import.meta.url resolves to the built chunk path in Astro 6 (site/dist/.prerender/chunks/),
making the old ../../.. depth land in site/ instead of the repo root.
Use process.cwd() which is always site/ when astro build runs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: adriens