fix(abut): 날개벽의 연직 헌치 삭제

- 위 연직 헌치(흉벽 배면)와 아래 연직 헌치(벽체 배면) 삭제. 관련 코드와 Haunch 타입 제거
- 저판 상면 헌치는 유지
- 테스트 갱신. 전체 637건 통과, 타입 검사·빌드 통과. 브라우저 시각 확인은 미실시

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

tests/abut-blocks-slab.test.ts

@@ -89,13 +89,8 @@ describe('교대 3D: 받침블럭과 접속슬래브 (spec §4.2, §4.8)', () =>
     for (const w of (named('wall') as THREE.Group).children) expect(new THREE.Box3().setFromObject(w).min.z).toBeGreaterThanOrEqual(members.shape.wallBackM - 1e-6);
   });
 
-  it('the upper 헌치 and the 접속슬래브 stay on the 브라켓 상면 over the back strip, not in it', () => {
+  it('the 접속슬래브 stays on the 브라켓 상면 over the back strip, not in it', () => {
     const backTop = (s: number) => members.parapetTopStartEl + ((members.parapetTopEndEl - members.parapetTopStartEl) * s) / model.length - members.shape.bracketHeightM;
-    for (const h of (named('haunches') as THREE.Group).children) {
-      const b = new THREE.Box3().setFromObject(h);
-      if (b.max.z < members.shape.parapetBackM + 1e-6) continue; // lower 헌치, behind the 벽체
-      expect(b.min.y).toBeGreaterThanOrEqual(Math.max(backTop(b.min.x), backTop(b.max.x)) - 1e-6);
-    }
     const pos = ((named('slab') as THREE.Group).children[0] as THREE.Mesh).geometry.getAttribute('position');
     for (let i = 0; i < pos.count; i++) {
       if (pos.getZ(i) >= members.shape.wallBackM) expect(pos.getY(i)).toBeGreaterThanOrEqual(backTop(pos.getX(i)) - 1e-6);