feat(core): rebar common rules (plan C1) and bearing-block bars (plan C2)

- C1: development length l_d = 0.6·d_b·fy/(λ√fck), splice 1.3·l_d, standard
  hooks (main 90°, tie 90°, stirrup 135° as written in the spec). fck 27 and
  fy 400/500 are marked as assumed values (I02).
- C2: bearing-block bars, one block per bearing (배치 분리). Bars S1 and S2 at
  @125 with 8 bars per 1200 mm side (7 gaps = 875, ends 162.5), 2500 mm long,
  coping embedment from the block height (pad included, Q16 결정).
- Tests: development and splice lengths; hook table limits; embedment 600 /
  550 / 619.1 / 569.1; P1 has 80 bars each of S1 and S2 over 10 blocks.
- Not yet: the ③ screen and the drawing check against the bearing-block drawing.

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

tests/rebar-common.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest';
+import { developmentLength, hookLength, MATERIAL_DEFAULTS, spliceLength } from '../src/core/rebar/common';
+
+describe('③ 공통 규칙 (spec §6.2, plan C1)', () => {
+  it('fck and fy defaults are assumed values (I02)', () => {
+    expect(MATERIAL_DEFAULTS.fck).toBe(27);
+    expect(MATERIAL_DEFAULTS.fy.H).toBe(400);
+    expect(MATERIAL_DEFAULTS.fy.S).toBe(500);
+    expect(MATERIAL_DEFAULTS.assumed).toBe(true);
+  });
+
+  it('development length follows l_d = 0.6·d_b·fy/(λ·√fck)', () => {
+    // H19, SD400, fck 27: 0.6 × 19 × 400 / √27
+    expect(developmentLength(19, 400, 27)).toBeCloseTo((0.6 * 19 * 400) / Math.sqrt(27), 9);
+    expect(developmentLength(19, 400, 27)).toBeCloseTo(877.6, 0);
+  });
+
+  it('splice length is 1.3 × l_d', () => {
+    expect(spliceLength(19, 400, 27)).toBeCloseTo(1.3 * developmentLength(19, 400, 27), 9);
+  });
+
+  it('hook lengths: main bars D25 or less 15.5 d_b, D29–D35 16.5 d_b; ties D16 or less 8.5 d_b', () => {
+    expect(hookLength('main90', 25)).toBeCloseTo(15.5 * 25, 9);
+    expect(hookLength('main90', 29)).toBeCloseTo(16.5 * 29, 9);
+    expect(hookLength('tie90', 16)).toBeCloseTo(8.5 * 16, 9);
+    expect(() => hookLength('main90', 40)).toThrow('없는 지름');
+    expect(() => hookLength('tie90', 19)).toThrow('없는 지름');
+  });
+
+  it('135° stirrup hook as written in the spec: 2.5·d_b·(3π/4) + 6·d_b', () => {
+    expect(hookLength('stirrup135', 16)).toBeCloseTo(2.5 * 16 * ((3 * Math.PI) / 4) + 6 * 16, 9);
+  });
+});