Adds `skald dedup --story <id>`: reads a story's most recent
prose-audit findings and walks every chapter, handing the author
the chapter prose + the findings with instructions to rephrase
ONLY the flagged repetitions (each recurrence made distinct) and
fix flagged continuity errors — everything else stays verbatim.
A surgical dedup, not a rewrite. Overwrites body_md, clears
body_md_tts so the chapter is re-prepped before narration. High
effort (prose-craft). Migration 0011 adds the 'dedup' run kind.
Completes the QC loop: audit (find) -> dedup (fix) -> re-audit.
