Second parity slice of #35.
- /mrs/new picks source and target from the repo's branches and dispatches mr create; the merge requests list links to it
- A refusal returns the draft with the command's own message, so a bad branch or a missing title does not cost the description
- Fork sources stay CLI-only for now; the form names the command
e2e covers the form's branch options, a refusal keeping title and body, and a successful create landing on the new merge request. The wiki's Parity page is updated.
Ref #35