Merge lane: jaah

Merge lane run: batch the queued PRs, run the full gate (if any) once on their merged tree, and merge the batch when it is green. Filed by the control plane (`app/merge_lane.py::ensure_lane`).

Merged 9 PRs (#5945–#5953) to develop in 6 quick-gated batches, all green (5775 tests); none ejected. develop head 3927288fc. Stale develop_red (0bf03ca) is a compose-stack start failure in the base check, not code.