Merge lane console: read-only lane runs

Goal: an operator watching the merge lane in the console always sees where it stands. Lane runs look like script runs, not editable Claude tasks, and nothing hides the outcome. The items below are goals, not literal steps: decline any with a reason. 1. A script-persona (merge lane) task page: - shows its body read-only, with no Depth, Involvement or persona controls; - shows no "Rate result" stars. 2. States read true: - An `active` lane run with no slot says something like "Running · no slot", not "Starting". - On a finished run, the Timeline's "Runner started" row drops or dims its live-looking "Running" chip. 3. Stop lane never traps the lane: - Switching the lane back on after a stop does not leave a paused run that blocks new runs. At minimum, the tab says "Stopped — Start the run to resume". - Stop's success notice survives a re-render until it is dismissed. 4. The Merge lane tab is reachable without "More ▾" while the lane is Active or Draining. At phone width, the five subtabs fit in one row or two balanced rows. 5. Runs list, desktop side pane at 1440px: - A run with many PRs (12 seen live) keeps its outcome fully readable: show the outcome first, or collapse the PR list to a count. - Hide a 0s active time. 6. The "Auto-merge armed outside the lane" banner shows when the last sweep ran (`projects.merge_lane_sweep.at`). The branch name renders as secondary text. Out of scope: lane batching, gate and merge logic; the outcome text the CP composes; forge call costs (Merge lane backend task). Done means: - Screenshots of the changed surfaces at desktop and at ≤480px. - ProjectMergeLaneTab vitests cover the long-batch case and the sweep time. - `./dc check full` is green. Consolidates drafts 6861, 6907, 6920 and items 2–3 of 6919 (Task 6937).

All six items shipped to develop: my first commit landed via #5746; develop's `held` lane state replaced stopped_run_id. 107 API + 233 web tests pass on develop. PR #5736 closed, empty after rebase. Follow-up draft 6967.