Parses .spec/decisions/*.md ADR files.

parse_file/2 is a semver-stable public function. Its return shape is a map with string keys "file", "title", "meta", "sections", "parse_errors", "parse_warnings", and "findings". That shape is unchanged within a major version.

Frontmatter fields change_type, supersedes, replaces, and reverses_what are parsed and ignored: they produce no finding. README documentation of this commitment lands at publish (L12); the commitment is recorded here.