Adds 'paper-lab-seed <file.md>' one-shot CLI that parses a draft's
References footer into the sidecar, so finalizeDoc produces a full
bibliography even when the LLM wrote the citations in plain text without
[N](doi:...) inline markers.

DOI extraction accepts Lancet/Cell-style parens. Overwrite guard
prevents silent clobbering of CrossRef-resolved sidecars. Duplicate [N]
detected and warned.