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 PR #6701 (task 9182) → develop 476bb9c9 after quick gate green (6003 passed; 52s, gate 34s). No ejections. Queue empty. Stale develop_red test (pre-merge-selection-selftest) re-run on develop: 43 passed. Memory: none applied.