feat(abut-rebar): ③ 교대 접속슬래브 3D 철근 (R1–R8)

- 접속슬래브 배근 경로를 교대 3D 철근에 추가 (선택 · 색 기준 공통)
- 콘크리트 안 검사에 접속슬래브 포함: 모든 교대 철근 (P10 다웰 포함) 밖으로 나간 점 없음

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

src/main.ts

@@ -697,7 +697,7 @@ function setupScene(): void {
     state.scene = scene;
     setView(state.view);
   }
-  // ③ 교대 (2026-11-04): with the piers hidden, the selected abutment's 저판 · 벽체 · 흉벽 · 날개벽 rebar is the ③ rebar (표 · 3D 선택 공통).
+  // ③ 교대 (2026-11-04): with the piers hidden, the selected abutment's 저판 · 벽체 · 흉벽 · 날개벽 · 접속슬래브 rebar is the ③ rebar (표 · 3D 선택 공통).
   const abutRec = piersShown(state.stage, state.abutActive) ? undefined : state.abutments.find((a) => a.name === state.abutActive);
   const abutGroup = abutRec ? abutGroupByName.get(abutRec.name) : undefined;
   const footing = abutRec ? abutFootingBuilt(abutRec) : null;
@@ -705,7 +705,7 @@ function setupScene(): void {
     const wall = abutWallBuilt(abutRec, footing.result);
     const para = wall ? abutParapetBuilt(abutRec, wall) : null;
     const wings = abutWingsBuilt(abutRec, footing.result).map((w) => w.result);
-    rebar3d = buildAbutRebar3D(footing.geom, footing.result, footing.skewK, footing.backM, footing.bottomEl, wall?.result, para?.result, wings);
+    rebar3d = buildAbutRebar3D(footing.geom, footing.result, footing.skewK, footing.backM, footing.bottomEl, wall?.result, para?.result, wings, abutSlabBuilt(abutRec)?.result);
     rebar3d.group.applyMatrix4(abutGroup.matrix);
     rebar3d.group.visible = state.stage === 'rebar';
     rebar3d.setColorMode(state.rebarColor);