land gate: bring landShared back under 4 minutes #598

The landShared budget was raised 300 -> 360 -> 420 s; the measured worst case was 382.5 s, which breaks the owner's rule that no test command takes 5 minutes.

Profile of one shared land (quiet machine, load ~3): package build 12 s, site build 135 s (881 pages: 63 s of it rendering 880 social cards, ~55 s Astro render), unit ~0, components 75 s, route sweep 126-139 s.

Plan: (1) cache rendered OG cards outside the checkout (shared by every worktree), 4 at a time; (2) run the site build beside the unit and component tests; (3) thin the docs routes of a full land sweep to the fewest pages that still render every component folder, keeping the pages the diff changed; the full sweep stays at release (test:full); (4) set landShared to 240 s in its own commit with the measurement.