Merge lane Runs tab: sort polish

Seen while doing the visual check for Task 7108 on the project's Merge lane › Runs tab. 1. The sort arrow on the Merge head butts against the next head ("MERGE▼AGE"); give a sorted head's arrow room so it never touches the neighbouring label (generic `ui/feed/FeedList` column header). 2. While the Runs list is sorted by Merge, the subtab still says "Runs 4" though only the 3 runs that merged are listed; say how many the sorted view shows (e.g. "3 merged"). 3. The Runs sort lives in component state, so a reload or shared link drops it; keep it in the URL as other sortable lists do (`hooks/useListPage`). Out of scope: the lane's gate, merge logic and filing. Done means: - Each item is visible on the Runs tab and covered by a web test, or declined with a reason.

Runs tab sort: arrow clear of the next head, "Runs N merged" subtab count, sort kept in the URL. Web tests added, quick gate green, visual check good at 1280px and 390px. Merged in PR #5824 (28da6eb9); its deploy was superseded by a later develop deploy. Follow-up draft #7171 filed.