PERF.32 CivilCraft: every survey point is painted every frame (13 s a paint, 4.2 s per a Discord member frame at 500k points)

scene.js:88 to view.js:175 paints all survey points on each frame: 13 s per paint and 4.2 s per a Discord member frame at 500k points, 1.2 s at the LAS import's 106k. Contours and labels add to it: contours(1) takes 6.7 s for 10,788 lines at 500k (string keys; 20,949 lines on the LAS), and labels call measureText plus fillText per frame (a 32 s paint on the LandXML scene). Change: a cached Path2D or bitmap per zoom bucket, decimation by zoom, a grid in-view test, integer keys in the contour tracer, label layout cached per bucket. Target for 500k: open under 5 s, zoom p95 under 100 ms.