POST /tasks/{id}/pr used to push the branch as-is, so uncommitted
worktree changes never reached the PR (empty diff). Now, after all
skip checks pass, the endpoint commits the worktree on host/<task>
(guarded: refuses when the worktree is on another branch), cleans
__pycache__/*.pyc like host.py merge does, and falls back to the
cloud identity when no git identity is configured. Nothing-to-commit
proceeds. Docs corrected: PR comes after status-merge and before
any local git merge (which deletes branch+worktree).
