Merge conflicts on reviewed pull requests go to the agent

When a reviewed pull request is approved but conflicts with main, Obeya no longer stops with git commands for resolving it by hand. The card's agent merges main into the pull request, resolves the conflict, runs the checks and leaves a note for the contributor. Obeya then pushes that and merges on the approval already given. If the contributor does not allow edits by maintainers, the agent writes the conflict up as a finding for them instead.