feat(rebar): bar-group bubbles and the length dimension on the coping 정면 (시안 ③)

- Nine bubbles (C1–6, C12·13, C9, C10, C11, C7·8, C14, C15, C16), each with a
  leader to the middle of its bars.
- The top dimension 300 · 18@250=4500 · 8@300=2400 · 18@250=4500 · 300, drawn
  only when it adds up to the coping length.

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

tests/coping-rebar-svg.test.ts

@@ -41,3 +41,17 @@ describe('단면 · 폐합 글자 겹침 (승인 2026-10-26)', () => {
     expect(labels).toBe(names.size);
   });
 });
+
+describe('정면 번호 풍선과 치수 (승인 2026-10-26, 시안 ③)', () => {
+  const svg = copingFrontSvg(scene.records, model.copingL * 1000);
+  it('has one bubble per bar group, with its label', () => {
+    for (const label of ['C1–6', 'C12·13', 'C9', 'C10', 'C11', 'C7·8', 'C14', 'C15', 'C16']) {
+      expect(svg).toContain(`>${label}<`);
+    }
+  });
+  it('writes the 시안 length dimension (300 · 4500 · 2400 · 4500 · 300 = 12000)', () => {
+    expect(svg).toContain('18@250=4500');
+    expect(svg).toContain('8@300=2400');
+    expect(svg).toContain('코핑 길이 12000');
+  });
+});