- Added `HASHLINE_CONTENT_SEPARATOR` and switched hashline formatting to colon separators across hashline helpers.
- Updated hashline prefix regexes in `edit/modes/hashline.ts` to require `:` and stop accepting tab separators.
- Updated `read.ts` and `write.ts` hashline prepending/stripping to match `LINE+ID:` content prefixes.
- Updated `match-line-format.ts` and hashline read-mode docs to document and emit `LINE+ID:content` lines.