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>

tests/validate-and-foundation.test.ts

@@ -92,7 +92,7 @@ describe('bearing and block checks (spec §10 W03, W04)', () => {
   it('W03 when a bearing centre is closer than half a block width to a step boundary', () => {
     const m = buildPier(loadP1());
     const boundary = m.segments[1].s0;
-    const bearings = m.bearings.map((b, k) => (k === 0 ? { ...b, s: boundary + 0.3 } : b));
+    const bearings = m.bearings.map((b, k) => (k === 0 ? { ...b, g: boundary + 0.3 } : b));
     const issues: Issue[] = [];
     validatePier(loadP1(), { ...m, bearings }, issues);
     expect(issues.map((i) => i.code)).toContain('W03');
@@ -100,7 +100,7 @@ describe('bearing and block checks (spec §10 W03, W04)', () => {
 
   it('W04 when a block footprint extends past the coping end', () => {
     const m = buildPier(loadP1());
-    const blocks = m.blocks.map((b, k) => (k === 0 ? { ...b, s: 0.1 } : b));
+    const blocks = m.blocks.map((b, k) => (k === 0 ? { ...b, g: 0.1 } : b));
     const issues: Issue[] = [];
     validatePier(loadP1(), { ...m, blocks }, issues);
     expect(issues.map((i) => i.code)).toContain('W04');