--format md|org on issue and merge request create, edit and comment.
The body still travels in stdin; the flag is sent only when a format was
chosen, so omitting it leaves the server's own default alone.
Editing an existing body starts on the format that body was stored in. That is the point of the row: an org body opened under a markdown picker and saved unchanged would silently become markdown, and its tables and links would flatten. New bodies and new comments start on markdown, and a comment does not inherit the parent's format — different author, different choice.
Rendering follows. Bodies and comments now render through the format they were stored with rather than through markdown unconditionally, so choosing org produces org on the screen that offered the choice. Comments carry their own stored format, which the issue and merge request comment models had not been decoding. Diff-line comments are untouched: the server has no format column for them and they are always markdown.
Releases are out of scope — release create and release edit take the
same flag, but there is no parity row for release markup, so the shared
compose sheet takes the format control as optional and that screen passes
none.
Closes the last two parity rows: choose body markup, on merge requests and on issues.