PERF.36 DetailCraft: every edit recomputes everything: autopilot, a quadratic clash check, a full scene of 1,925 draw calls, two JSON snapshots, linear model scans

Measured in /use 0.8.1 and in Node (tools/perf/apps3d-detailcraft.mjs, apps3d-detail-node.mjs; 2,820-member grid24x12x5 and the new 10x grid48x30x10 with 28,500 members and 100x grid60x60x40 with 285,600 members): refresh() (detailcraft.js:354) after any change runs build 151 ms, markParts 261 ms, autopilot.propose 899 ms (18 times more for 6.2 times the members), clashCheck 10.2 s (quadratic), and rebuilds the whole three.js scene with a Mesh plus an EdgesGeometry per part (1,925 draw calls for 948 parts); Model.change stringifies the state twice (model.js:165/170; 20 MB at 10x, 197 MB at 100x) and undo re-parses all of it; Tx.addHole and addConnection find by find/some (model.js:349, :376), so pasting the 10x model took 2.6 s and building the 100x file 716 s. Change: incremental build by id, patch-based undo (the whole-document snapshot row), an instanced or merged scene, id maps in the model API, clash check through a grid. Healthy: build, marks, drawings and IFC export are near linear.