scripts/reflow_md.py joins hard-wrapped markdown prose to one line per
paragraph, leaving code fences, tables, headings, blockquotes, and front
matter byte-identical, and refusing to touch any file whose non-whitespace
token sequence would change (so it can only ever edit whitespace). Add
`make reflow-docs` (apply) and `make reflow-check` (fail if any in-scope doc
is hard-wrapped), and wire reflow-check into `make quality` so CI keeps the
manual ~75-char line breaks from creeping back in.
