Jujutsu VCS Workflow

Agents use jj as the primary local VCS interface while preserving Git compatibility for Gitea. Initialize colocated jj, use jj new and jj bookmark set for branches, jj describe for commits, jj git export before Git/Gitea operations, and jj git push --bookmark for pushes. Persist jj_change_id and jj_operation_id in recovery manifests.