Fetch the full SKILL.md content and metadata for a single artifact. Provide EXACTLY ONE of `artifactId` (the UUID returned by `search`) or `slug` (the URL-safe identifier, e.g. from a `/p/<slug>` link). Passing both or neither returns a `validation_failed` error. Use this after `search` to retrieve the body of a hit the user wants to read, summarize, apply, or fork. Returns the artifact's name, description, type, contributor, version, timestamps, the full SKILL.md text (YAML frontmatter + markdown body, up to 256 KB), the number of bundled extras (`bundledCount`), their filenames (`bundledFilenames`), per-file metadata in `bundledFiles` (each entry has `key`, `filename`, and `originalRef` — the EXACT body-relative reference string the importer matched, or `null` when the file was bundled without a body reference; use this to translate a link span in the body back to its bundle filename), and the public-surface fields `slug`, `authorCredit`, `industries`. To fetch a bundled extra, read it as a resource at `artifact://<artifactId>/bundled/<filename>`.