Generate a per-rune intro record from each reference page and the rune's resolution

Acceptance Criteria

• Each rune with a reference page has one record with title, description, package, composed, status, schemaType and source, and no install field (D8)
• title, description and status are read from the reference page's frontmatter, not repeated anywhere else
• composed and source come from how the rune resolves on the main site: a composition's .md definition, or a native rune's schema file, as a repo-relative path
• schemaType is the type the rune's resolved schema row publishes with its defaults, the row refrakt inspect <rune> --site main prints; it is the default when an attribute changes the type or can switch it off, and empty when the rune publishes nothing (D9)
• The drift check fails when the committed data differs from a fresh run, as it does for the attribute data
• A test covers one core rune, one native plugin rune, one composed rune, and one rune that publishes no structured data