v0.29.0

• Read Markdown structure: --input-format markdown exposes a document body as a tree of heading sections carrying 1-based inclusive source line ranges, so a caller can splice exact source without reserializing Markdown or counting UTF-8 bytes
• Address an array element by its content instead of its position: a non-numeric path segment resolves against the field named by --slug-field, and matching several elements is an error naming the candidate indices rather than silently taking the first
• Accept --slug-field on set and unset as well as on reads, so an address that paths emits can be fed straight back to a write instead of failing on afdata's own output
• Refuse --input-format markdown while parsing argv on every mutating verb and on lint, so help and the CLI reference stop advertising a combination whose only outcome is failure
• Split three failures out of document_parse_failed: a malformed address is document_invalid_path, a file afdata declines to number is document_source_refused, and a contradictory argument is document_invalid_argument, each keeping the detail that says what to fix
• Complete keyed-array editing at the document root, so add and remove work with an empty KEY on a root-level JSON or YAML array