Perform comprehensive document normalization across the library, or over
named documents only.

Operations performed:
- Update link titles to match target document headers
- Adjust header levels for consistent hierarchy
- Renumber ordered lists
- Fix markdown formatting (newlines, indentation)
- Standardize list formatting
- Normalize document structure

With no `-k`, every document in the library is rewritten and frontmatter is
re-serialized along the way. With `-k`, only the named documents are touched,
frontmatter is left exactly as written, and the result is byte-identical to
what `iwe create` and `iwe update --content` produce — so a document
normalized this way matches one written through the CLI. One difference: a
named document is normalized on its own, without the rest of the library, so
its link titles keep the text they were written with. Only the unscoped run
refreshes them to match the target headers.