When triggered from an issue, Claude should create a branch for the issue and reuse it on subsequent tags on that same issue

Right now we delete the branch if Claude doesn't create a PR link. Instead we should keep it around and the next tag should reuse that branch if it's present. Claude should be aware of this (that it's reinvoked on the same branch as before). This way people can ask Claude to add more to the branch before creating a PR. @claude