feat(core,view): bent coping stage 2 — mitred coping, stretch-local bearings, blocks and columns

- buildPier builds on buildAxis: each object carries its stretch k and a local
  s from that stretch's base; coping parts are per stretch with the mitre plane
  trimming the overlap in the scene (renderer.localClippingEnabled).
- Straight P1 output is unchanged (regression tests pass).
- Bent coping is supported for 현장타설말뚝 only; footings and piles on a bent
  axis remain 미실시 until stage 3. Kink outside the coping and columns within
  the Level half-width of the kink are refused.
- W03/W04 use coping coordinates (g).
- Tests: constructed 60° bend — world coordinates of bearings, blocks and the
  column survive the stretch frames; mitre sides; scene mesh count; refusals.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

src/main.ts

@@ -71,6 +71,7 @@ function setStatus(msg: string): void {
 // --- 3D renderer -------------------------------------------------------------
 const container = $<HTMLDivElement>('canvas');
 const renderer = new THREE.WebGLRenderer({ antialias: true });
+renderer.localClippingEnabled = true; // mitre planes on the bent coping
 renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
 container.appendChild(renderer.domElement);
 const world = new THREE.Scene();