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 8 PRs to develop: #6587, #6586 (Dependabot, full gate), #6588, #6590, #6591, #6592, #6593. Ejected #6589: conflicts with develop (dirty), sent back to its runner to rebase. Queue empty; develop not red. Last batch took 73s (gate 26s). Memory: none applied.