feat(trail): name the trail an update through a change writes to; -n on list

trail update with no selector, --branch, or <repo>/<n> writes the parent project trail, whose fields every change shares. It now says so on stderr before the PATCH:

Updating trail #42 "Title" (parent of cli/1503); these fields apply to the whole trail, not just this change.

trail list and trail timeline take -n for --limit, like trail finding.