Reapply "feat(rebar): B1–B4와 B5–B8 방향 교환 (B1–B4는 W 방향, B5–B8은 L 방향)"

사용자 요청으로 방향 교환을 다시 적용 (99db6a1 되돌림). 격자 키 sL/sW, 3D·단면·철근표 역할과 테스트 기대값이 교환 기준으로 돌아감.

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

tests/rebar-summary.test.ts

@@ -35,21 +35,21 @@ describe('③ 철근표 요약 (P1)', () => {
     expect(count('P6')).toBe(32);
   });
 
-  it('footing: B1–B4 31 each, B5–B8 40 each, B10-1 16, B10-2 16, B11 30, B12 24 (k = 8)', () => {
-    for (const n of ['B1', 'B2', 'B3', 'B4']) expect(count(n)).toBe(31);
-    for (const n of ['B5', 'B6', 'B7', 'B8']) expect(count(n)).toBe(40);
+  it('footing (방향 교환): B1–B4 40 each, B5–B8 31 each, B10-1 16, B10-2 16, B11 30, B12 24 (k = 8)', () => {
+    for (const n of ['B1', 'B2', 'B3', 'B4']) expect(count(n)).toBe(40);
+    for (const n of ['B5', 'B6', 'B7', 'B8']) expect(count(n)).toBe(31);
     expect(count('B10-1')).toBe(16);
     expect(count('B10-2')).toBe(16);
     expect(count('B11')).toBe(30);
     expect(count('B12')).toBe(24);
   });
 
-  it('B9: 306 bars (320 on the grid less 14 in the column zone); warnings: B2 needs a splice (13646 > 12000)', () => {
+  it('B9: 306 bars (320 on the grid less 14 in the column zone); warnings: B6 needs a splice (13646 > 12000)', () => {
     expect(count('B9')).toBe(306);
     expect(warnings.map((w) => w.code)).toEqual(['I02', 'RB-S04', 'RB-F08']); // defaults are assumed values (I02); bearing embedment 619–669 < 882 (RB-S04)
-    expect(warnings.find((w) => w.code === 'RB-F08')!.bar).toBe('B2');
-    // 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);
+    expect(warnings.find((w) => w.code === 'RB-F08')!.bar).toBe('B6');
+    // B6 is split into two pieces (추천안): each piece is about half the 13646 bar plus half the lap.
+    expect(rows.find((r) => r.name === 'B6')!.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', () => {