Generate a /libraries/[slug] route from the registry so every library has
an internal page showing its docs, repository, installation commands,
getting-started steps and a copyable agent setup prompt.

Detail content lives in data/library-details/, one file per slug, and is
keyed to the registry by a test that asserts the two sets agree in both
directions, so a missing entry fails loudly instead of 404ing silently.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>