PERF.76 Code: O(n squared) searches in kernel code (ModelCraft mesh ops, the shared m3d model, CivilCraft LandXML) and render functions that rebuild whole panels

Nested-loop searches with includes/some inside N by N loops: modelcraft mesh/ops.js:421 subdivide (also :471, :820, :915), m3d model.js:693, :778, :1637, :1957 (in both ModelCraft and CadCraft's copy), civilcraft landxml.js:298-322. These are the places a 10x model turns into a 100x wait; the 3D track's numbers (ModelCraft push/pull and undo at 500k faces) land here. Change: Sets and Maps keyed by vertex or id, measured before and after with tools/perf/scale-bench.mjs and the apps3d scripts. Render functions that rebuild and re-query the DOM on every call (196 querySelectorAll and 315 addEventListener inside render functions; takeoffcraft.js sheet list on every sheet switch, shell app-workspace.js, supercadcraft.js, cadcraft renderLayers and renderSelTotals): keyed children and incremental updates, measured on the 2D track's 2,000-sheet set.