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>

tests/coping-rebar-svg.test.ts

@@ -34,11 +34,12 @@ describe('코핑 배근 정면 · 단면 (승인 2026-10-26)', () => {
 });
 
 describe('단면 · 폐합 글자 겹침 (승인 2026-10-26)', () => {
-  it('writes each bar name once, and each spot once', () => {
-    const svg = copingSectionSvg(scene.records, 6);
-    const labels = (svg.match(/<text /g) ?? []).length;
-    const names = new Set((svg.match(/font-size="120"[^>]*>(C\d+)</g) ?? []).map((s) => s.replace(/.*>/, '')));
-    expect(labels).toBe(names.size);
+  it('writes each bubble label once', () => {
+    const svg = copingSectionSvg(scene.records, 6, model.copingRefTop, model.copingB * 1000);
+    // A bubble is drawn for each group that is cut at this station, and only once.
+    for (const label of ['C1–6', 'C12·13', 'C10', 'C7·8', 'C14', 'C16']) {
+      expect(svg.split(`>${label}<`).length - 1).toBe(1);
+    }
   });
 });