Recover nesting for style-only lists (List Bullet 2 / List Number 2 without numbering refs)

[Tishinator]

Problem

Lists built purely from paragraph styles like List Bullet 2 / List Number 3 — with no numPr/ilvl numbering references — convert as flat, separate lists instead of nested ones. Real Word-authored lists carry numbering definitions and nest correctly; this only affects documents where the style alone implies the level. See the degraded.docx fixture ("Style-only lists" section) and decision log D12.

Proposed fix

Extend src/docx2md/preprocess.py (same technique as the monospace→code pre-pass):

1. Detect paragraphs whose pStyle matches List (Bullet|Number)( \d)?.
2. Inject a multilevel abstractNum/num definition into word/numbering.xml (the fixture generator in scripts/make_fixtures.py already builds exactly this XML).
3. Stamp numPr with numId + ilvl derived from the style suffix onto those paragraphs, one numId per contiguous list group.

Pandoc then nests correctly — verified during the feasibility spike.

Acceptance

• New fixture with style-only nested bullet + ordered lists converts with correct nesting.
• Existing lists.docx golden output unchanged.
• Remove the corresponding entry from README known limitations.

Priority: highest of the known issues — it is the only one that loses document structure rather than styling.