feat(core): lengths for coping, column and the B2 split (추천안)

- Coping: C9/C10 lower U = 1740 + 2h with h linear along the slope and 2300 on
  the Level (3522 / 6098 / 6249 / 6340 from the document); C12 (3717–10183),
  C13 11746, C14 3447.5, C15 3852, C16 4070.
- Column: P3 = C_t + 1.3·l_d(H19) lap (추천안 for Q-C6, lap 1146.6), P5 = C_t.
- Footing: B2 13646 is split into two pieces at a splice with 1.3·l_d(S25,
  SD500) (추천안 for Q-B6), piece ≈ 7776 each.
- Not done: C9/C11 cap (삿갓) lengths (Q-K5 open), P1/P2 per-line pieces.
- Tests against the document values; P1 summary updated.
- Not verified in a browser.

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

tests/rebar-summary.test.ts

@@ -46,6 +46,16 @@ describe('③ 철근표 요약 (P1)', () => {
   it('B9: 320 bars; warnings: B2 needs a splice (13646 > 12000)', () => {
     expect(count('B9')).toBe(320);
     expect(warnings.map((w) => w.code)).toEqual(['RB-F08']);
-    expect(rows.find((r) => r.name === 'B2')!.length!).toBeGreaterThan(12000);
+    // B2 is split into two pieces (추천안): each piece is about half the 13646 bar plus half the lap.
+    expect(rows.find((r) => r.name === 'B2')!.length!).toBeCloseTo(7776, 0);
+  });
+
+  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);
+    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);
+    expect(rows.find((r) => r.name === 'P5')!.length).toBeCloseTo(5657.7, 0);
+    expect(rows.find((r) => r.name === 'P3')!.length!).toBeCloseTo(5657.7 + 1146.6, 0);
   });
 });