fix(view): ③ 철근배근도 선택한 구조물만 3D에 표시

- 교각을 선택하면 교대를 숨김(②와 같은 규칙). 교대 선택 시 교각 숨김은 기존대로
- ① ↔ ③ 전환 때도 장면을 다시 만들어 표시 규칙이 바로 반영되게 함

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

src/core/abut/visibility.ts

@@ -2,7 +2,7 @@
  * What the 3D view draws for the selection (2026-11-03, 형상계획 ②).
  * In ② only the selected object is drawn: a selected abutment hides the piers, and a selected pier hides the abutments.
  * In ① (형상 생성) the abutments are always drawn, as before; the piers follow 전체 보기 in ①, not this rule.
- * In ③ (2026-11-04, 교대 배근) a selected abutment is drawn alone too; with a pier selected, ③ draws as before.
+ * In ③ (2026-11-04) only the selected object is drawn too, the same as ②: a selected pier hides the abutments.
  */
 
 /** True when the pier scene (and its rebar) should be built for this stage and selection. */
@@ -12,7 +12,6 @@ export function piersShown(stage: string, abutActive: string | null): boolean {
 
 /** True when the abutment with this name should be drawn. */
 export function abutShown(stage: string, abutActive: string | null, name: string): boolean {
-  if (stage === 'rebar') return abutActive === null || name === abutActive;
-  if (stage !== 'plan') return true;
+  if (stage !== 'plan' && stage !== 'rebar') return true;
   return name === abutActive;
 }