feat(rebar): 단면·폐합 section with the top-row and side-row chains and bar-group bubbles

- Top row (C1–C8) spacing along the 교축 from chainDims, between the coping's
  two long edges (±B/2).
- Side rows (C12·C13) along the EL, from the coping top EL down to the lowest
  side bar.
- One bubble per bar group cut at the station, with a leader to its bars.

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

src/main.ts

@@ -1107,7 +1107,7 @@ function renderCopingDrawings(box: HTMLDivElement, pier: Pier): void {
     const label = el('label', '단면 위치 s (m, 코핑 시작에서) ');
     label.appendChild(station);
     wrap.appendChild(label);
-    fig.innerHTML = copingSectionSvg(rebar3d.records, at);
+    fig.innerHTML = copingSectionSvg(rebar3d.records, at, pier.model.copingRefTop, pier.model.copingB * 1000);
     fig.appendChild(el('figcaption', `단면 · 폐합 구성 · s = ${at} m에서 자른 철근 (C9–C11 폐합 포함)`, 'muted small'));
   }
   wrap.appendChild(fig);