MC-4744

Pre-existing mobile bug discovered while fixing MC-4736 (Tasks page clipping). The Run history page (/runs) renders a wide data table (.runs-table, ~600px) that does NOT collapse to a mobile card layout the way the Tasks page table does. On a 360px viewport this overflows the document horizontally by ~248px, so the page scrolls sideways and the run titles are clipped on the left. Confirmed pre-existing and unrelated to the MC-4736 fix via A/B test (the overflow is present even with the MC-4736 CSS changes stashed). MC-4736 only touched the shared filter-tab row (now wraps correctly on /runs too); the .runs-table itself was left untouched and remains non-responsive. Fix direction: mirror the Tasks page approach — transform .runs-table into stacked cards under @media (max-width: 768px) in templates/runs.html (the Tasks page does this in templates/tasks.html lines ~962-1065). Add a Playwright check at 320/360/390/412px for no horizontal document scroll on /runs (reuse the pattern in tests/test_mc4736_tasks_mobile_layout.py). Repo: mission-control (templates/runs.html, static/style.css). Priority: low — cosmetic mobile overflow, page is still usable via sideways scroll.