feat(quantity): ④ 전체 합계에 교량 전체 집계 표를 추가

- 교각 목록의 "전체"를 "전체 합계 (N기)"로 표시
- 전체를 고르고 2기 이상이면 강종·직경별 교량 전체 집계를 맨 위에 표시 (소계, 합계, 할증 포함, 커플러)
- 집계 규칙을 core/quantity-total.ts로 분리하고 테스트 3건 추가. 교각별 표는 그대로

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

tests/quantity-total.test.ts

@@ -0,0 +1,41 @@
+import { describe, expect, it } from 'vitest';
+import { aggregateQuantities } from '../src/core/quantity-total';
+import type { Quantity } from '../src/core/rebar/quantity';
+
+/** A 재료표 with one 강종·직경 line; only the fields the aggregate reads are filled. */
+function quantity(grade: number, size: string, count: number, totalM: number, kg: number, extra: Partial<Quantity> = {}): Quantity {
+  return {
+    groups: [{ grade, kg, diameters: [{ size, dMm: 19, lines: [{ count } as never], totalM, kg }] }],
+    couplers: [],
+    missing: [],
+    kg,
+    wastePercent: 0,
+    kgWithWaste: kg,
+    ton: kg / 1000,
+    ...extra,
+  };
+}
+
+describe('aggregateQuantities (교량 전체 집계)', () => {
+  it('sums the same 강종·직경 over the piers', () => {
+    const total = aggregateQuantities([quantity(400, 'H19', 10, 100, 225), quantity(400, 'H19', 5, 50, 112.5)]);
+    expect(total.rows).toEqual([{ grade: 400, size: 'H19', count: 15, totalM: 150, kg: 337.5 }]);
+    expect(total.kg).toBe(337.5);
+  });
+
+  it('keeps different 강종 and 직경 apart and orders them by 강종 then 직경', () => {
+    const total = aggregateQuantities([quantity(500, 'S19', 4, 40, 90), quantity(400, 'H25', 2, 20, 50), quantity(400, 'H19', 1, 10, 22.5)]);
+    expect(total.rows.map((r) => `${r.grade}|${r.size}`)).toEqual(['400|H19', '400|H25', '500|S19']);
+    expect(total.gradeKg).toEqual([{ grade: 400, kg: 72.5 }, { grade: 500, kg: 90 }]);
+  });
+
+  it('adds the 할증 total and the couplers across the piers', () => {
+    const total = aggregateQuantities([
+      { ...quantity(400, 'H19', 1, 1, 100, { kgWithWaste: 110, couplers: [{ name: '커플러 H19', count: 3 }] }) },
+      { ...quantity(400, 'H19', 1, 1, 200, { kgWithWaste: 220, couplers: [{ name: '커플러 H19', count: 2 }] }) },
+    ]);
+    expect(total.kgWithWaste).toBe(330);
+    expect(total.ton).toBeCloseTo(0.33, 6);
+    expect(total.couplers).toEqual([{ name: '커플러 H19', count: 5 }]);
+  });
+});