fix(view): 교대만 그려진 상태에서 정면·측면·평면 버튼이 동작하도록 함

- 원인: 교대를 고르면 교각 장면이 없어서 setView가 바로 반환. 정면 버튼이 아무 동작도 하지 않았음
- 교대만 보일 때는 교대 그룹의 좌표계(+x = 교대축, +z = 전면)에서 카메라 방향을 잡고, 보이는 교대 전체를 맞춤
- 테스트 640건 통과, 타입 검사·빌드 통과. 브라우저 시각 확인은 미실시

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

src/main.ts

@@ -479,9 +479,12 @@ function setView(kind: ViewKind): void {
   $('views-toggle').textContent = `${VIEWS.find((v) => v.kind === kind)?.label ?? ''} ▾`;
   setMenuOpen('views', false);
   const scene = allPiers ? allPiers.view : state.scene;
-  if (!scene) return;
   const pier = activePier();
-  if (!pier?.model) return;
+  if (!scene || !pier?.model) {
+    // No pier is drawn (an abutment is selected in ②): the views follow the abutment's own frame (2026-11-03).
+    abutView(kind);
+    return;
+  }
   const framed = viewPosition(scene, kind, pier.model);
   // Keep the chosen view direction but fit every model (piers and abutments) in the window (2026-11-03).
   const fitted = fitToModels(framed.position, framed.target);
@@ -490,6 +493,33 @@ function setView(kind: ViewKind): void {
   controls.update();
 }
 
+/** Camera for the drawn abutments alone: the directions come from the abutment group (local +x = 교대축 IP1→IP3, +z = 전면). */
+function abutView(kind: ViewKind): void {
+  const shown = abutGroups.filter((g) => g.visible);
+  if (shown.length === 0) return;
+  const box = new THREE.Box3();
+  for (const g of shown) {
+    g.updateWorldMatrix(true, true);
+    box.expandByObject(g);
+  }
+  const sphere = box.getBoundingSphere(new THREE.Sphere());
+  const ref = shown[0];
+  const axisX = new THREE.Vector3(1, 0, 0).transformDirection(ref.matrixWorld);
+  const front = new THREE.Vector3(0, 0, 1).transformDirection(ref.matrixWorld);
+  const lift = new THREE.Vector3(0, 0.15, 0);
+  const dirs: Record<ViewKind, THREE.Vector3> = {
+    iso: new THREE.Vector3(1, 0.7, 1).normalize(),
+    front: front.clone().add(lift).normalize(),
+    side: axisX.clone().add(lift).normalize(),
+    top: new THREE.Vector3(0, 1, 0.001).normalize(),
+  };
+  const target = sphere.center.clone();
+  const dist = sphere.radius * 2.6;
+  camera.position.copy(target.clone().add(dirs[kind].multiplyScalar(dist)));
+  controls.target.copy(target);
+  controls.update();
+}
+
 /** Bounding sphere of everything drawn (the piers or the all-piers view, plus the abutments) fitted to the camera. */
 function fitToModels(position: THREE.Vector3, target: THREE.Vector3): { position: THREE.Vector3; target: THREE.Vector3 } {
   const box = new THREE.Box3();