Astro: Unauthenticated Path Override via `x-astro-path` / `x_astro_path`

Summary The @astrojs/vercel serverless entrypoint reads the x-astro-path header and xastropath query parameter to rewrite the internal request path, with no authentication whatsoever. On deployments without Edge Middleware, this lets anyone bypass Vercel's platform-level path restrictions entirel...