A planner's "one more round" comment on a handed-over crew pull gives it back to its builder #6585

On #6507, the planner restated the review's ask as one concrete change, as the planner's rules allow, but the pull had been handed to a person, so no run started and it came back unchanged.

Done:

• [ ] A comment by the repository's planner agent on an open crew pull that is handed over (the hand-over note is its latest crew state), whose body starts with Planner, one more round, re-assigns the pull to the builder that opened it and starts its run, the same as "Give back to the crew".
• [ ] Anyone else's comment, or a pull not handed over, changes nothing.
• [ ] Tests: the planner's comment re-assigns and starts a run; another author's comment does not.

Files: the module that handles "Give back to the crew" in src/crew/, a test.