feat(rebar): select several bars on ③ and show only the selected ones (선택만 보기)

The 철근표 has a selection checkbox per row. Select-all / clear and 선택만 보기 sit above the table. In 선택만 보기 the other
bars are hidden in 3D and the members stay at 50% for context. A 3D click or an alert [보기] selects one bar; the
selection clears when the member tab or the pier changes. The selection is screen state and is not saved to the project.

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

tests/rebar3d.test.ts

@@ -74,15 +74,25 @@ describe('3D 철근 모델 (③)', () => {
     expect(rb.byName.get('띠철근 커플러')!.length).toBe(35);
   });
 
-  it('highlight dims the other bars and keeps the chosen one', () => {
-    rb.highlight('P3');
+  it('show dims the other bars and keeps the chosen one', () => {
+    rb.show(new Set(['P3']), false);
     const p3 = (rb.byName.get('P3')![0].material as THREE.MeshStandardMaterial).opacity;
     const c1 = (rb.byName.get('C1')![0].material as THREE.MeshStandardMaterial).opacity;
     expect(p3).toBe(1);
     expect(c1).toBeLessThan(1);
-    rb.highlight(null);
+    rb.show(null, false);
     expect((rb.byName.get('C1')![0].material as THREE.MeshStandardMaterial).opacity).toBe(1);
   });
+
+  it('선택만 보기: with isolate on, only the selected names stay visible; several names can be selected', () => {
+    rb.show(new Set(['P3', 'C1']), true);
+    expect(rb.byName.get('P3')!.every((m) => m.visible)).toBe(true);
+    expect(rb.byName.get('C1')!.every((m) => m.visible)).toBe(true);
+    expect(rb.byName.get('C9')!.every((m) => !m.visible)).toBe(true);
+    rb.show(null, true);
+    expect(rb.byName.get('C9')!.every((m) => m.visible)).toBe(true);
+    rb.show(null, false);
+  });
 });
 
 describe('받침블럭 S1 · S2 in 3D (받침블럭철근.md §3–5)', () => {