land gate: sweep representative atlas term pages, not all 269 #595

#572 adds 270 prerendered /atlas/ pages (one template, 269 terms). The route sweep runs each through desktop, mobile and axe (about 800 tests, 100+ s), which with the dist rebuild of #591 puts every full-sweep land over its 360 s budget (450 s measured on #572). The gallery already solves the same shape: E2E_GALLERY=representatives keeps a few item pages at land and test:full audits every one. Do the same for /atlas//: a handful of representative terms at land, all at test:full.