Merge lane Runs tab reads at a glance

Goal: the project's Merge lane › Runs tab shows real runs clearly and supports benchmarking from the UI. Goals, not steps; the lane changed a lot in Task 6722 (stacked runs deleted, a stopped run never holds the lane), so check what still applies first. Consolidates drafts 6971 and 6967 (item 3). Draft 6982 (act on a held lane) is obsolete: a stopped run no longer holds the lane. 1. Outcomes pluralise correctly ("1 PR"). 2. Long runs of identical "N PRs: N skipped" outcomes (e.g. while develop is red) collapse into one line with a count, or no run is filed when nothing changed, so real runs aren't buried. 3. Each run row shows start-to-last-merge time, so `docs/patterns/runner-efficiency-benchmarking.md` §Merge lane gate can be read off the tab. 4. At phone width two runs are distinguishable (short id, or age plus outcome). Out of scope: lane batching, gate and merge logic. Done means: - Each item visible on the Runs tab and covered by ProjectMergeLaneTab tests, or declined with a reason. - Screenshots at desktop and ≤480px. - `./dc check full` green.

Runs tab: "1 PR", identical skip runs collapse to one ×N row, Merge column (start→last merge), run id leads the title on phone. Quick gate + changed-area tests green; lane full gate merged #5775 (35198f0); deploy succeeded. Visual check done at desktop and 390px. Follow-up draft 7108.