feat(rebar): piece lengths for C9–C13 and P1·P2 so the 재료표 has no missing bars

A row can now carry pieces (length, count). C9, C10, C11 and C9·C11 사이 have U and 삿갓 pieces per position (3 loops each);
C12 and C13 have 일자 and ㄷ pieces per bar; P1 and P2 have their splice pieces, each counting all the bars. The
재료표 totals from the pieces, so no bar is left out. 개수 stays the 철근표 count; the piece count is kept beside it. The
삿갓 length h − 100 is an assumption (Q-K5) and is noted on the ④ screen.

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

tests/rebar-summary.test.ts

@@ -53,7 +53,8 @@ describe('③ 철근표 요약 (P1)', () => {
   });
 
   it('lengths from the documents: C13 11746, C14 3447.5, C15 3852, C16 4070, P3 ≈ C_t + 1.3·l_d, P5 ≈ C_t', () => {
-    expect(rows.find((r) => r.name === 'C13')!.length).toBe(11746);
+    // C13 has several lengths now: its straight bars are pieces (수정 2026-10-23); 11746 is the first 일자.
+    expect(rows.find((r) => r.name === 'C13')!.pieces!.some((p) => p.length === 11746)).toBe(true);
     expect(rows.find((r) => r.name === 'C14')!.length).toBe(3447.5);
     expect(rows.find((r) => r.name === 'C15')!.length).toBe(3852);
     expect(rows.find((r) => r.name === 'C16')!.length).toBe(4070);