feat(abut-rebar): ③ 교대 저판 3D 철근 (B1–B10)

- 배근 결과(abutFootingRebar)로 저판 철근을 교대 좌표에 그림: B1 ⊓ · B2 ⊔ · B3 · B4, B5 ⊓ · B6 ⊔ · B7 · B8, B9, B10-1 · B10-2, 옵션 ② B1-S · B2-S
- 교대 선택 시 ③ 철근(rebar3d)으로 사용: 철근표 · 삽도 선택, 선택만 보기, 색 기준, 3D 클릭 선택 공통
- 교각 rebar3d의 강조 · 색 · 범례를 rebarControls로 공용화
- 테스트: 철근표 개수 = 3D 개수, 모든 철근이 저판 안 (skew · 교대축 직각)

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

src/view/rebar3d.ts

@@ -49,7 +49,7 @@ const MEMBER_LABELS: Record<RebarMemberKey, string> = { bearing: '받침블럭',
 const hex = (v: number) => `#${v.toString(16).padStart(6, '0')}`;
 /** Rebar is drawn a little deeper than the 6.7 colours so it reads through the half-transparent members (승인 2026-10-23). */
 const REBAR_SHADE = 0.8;
-const rebarColor = (v: number) => new THREE.Color(v).multiplyScalar(REBAR_SHADE);
+export const rebarColor = (v: number) => new THREE.Color(v).multiplyScalar(REBAR_SHADE);
 
 const COLOR = {
   coping: 0xb4531f,
@@ -555,6 +555,11 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     }
   }
 
+  return { group, byName, records, ...rebarControls(byName) };
+}
+
+/** Highlight, colour and legend over bars grouped by 철근표 number (교각 · 교대 3D 철근 공통). */
+export function rebarControls(byName: Map<string, THREE.Mesh[]>): Pick<RebarScene, 'show' | 'setColorMode' | 'legend'> {
   const show = (names: ReadonlySet<string> | null, isolate: boolean) => {
     // 커플러 as a name selects every coupler bar.
     const isOn = (key: string) => names === null || names.has(key) || (names.has('커플러') && key.includes('커플러'));
@@ -592,5 +597,5 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     const items = DIAMETER_GROUPS.map((g, i) => ({ label: g.label, color: hex(DIAMETER_COLORS[i]) })).filter((_, i) => present.has(i));
     return present.has(-1) ? [...items, { label: '기타', color: hex(OTHER_COLOR) }] : items;
   };
-  return { group, byName, records, show, setColorMode, legend };
+  return { show, setColorMode, legend };
 }