atproto git client

feat(stack): add unlink, which takes pulls out of a chain master

`link` wrote `dependentOn` and nothing removed it, so a chain ordered wrongly had no exit inside the tool: `stack resubmit` cannot correlate members whose rounds carry no change-id, and `pr resubmit` refuses a member. Each named pull's dependent inherits its parent, in one atomic batch. Change-Id: Id26957a609c329a7b38a3194998225ab00385b76


+356
4 changed files