feat(core,view): footing rebar B1–B12 (plan C5) and the ③ rebar screen v1

- Footing (확대기초철근 (1).md): grid counts from W and L, layer heights,
  B1–B4 and B5–B8 counts and lengths (B2 13646, B6 11396), B10-1/B10-2,
  B11 (60) and B12 (47) with their lengths. B9 is not computed yet.
- rebarSummary: one 철근표 per pier from the model (bearing, coping, column,
  footing), with alerts: RB-F08 (B2 needs a splice, Q-B6), RB-F09 (B9 not
  computed).
- ③ screen v1: stage nav button, member tabs (받침블럭 · 코핑 · 기둥 · 확대기초),
  rebar table with 번호 · 규격 · 개수 · 길이 · 비고, alert list, and the open
  questions (Q-B5, Q-B6, Q-C9). Drawings and the 강조 연동 are not in v1.
- Tests: footing values from the document; P1 summary totals; warnings.
- Not verified in a browser.

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

tests/rebar-summary.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from 'vitest';
+import { buildPier } from '../src/core/geometry';
+import { rebarSummary } from '../src/core/rebar/summary';
+import { loadP1 } from './helpers';
+
+const { rows, warnings } = rebarSummary(buildPier(loadP1()));
+const count = (name: string) => rows.find((r) => r.name === name)!.count;
+
+describe('③ 철근표 요약 (P1)', () => {
+  it('bearing blocks: S1 and S2 80 bars each', () => {
+    expect(count('S1')).toBe(80);
+    expect(count('S2')).toBe(80);
+  });
+
+  it('coping: C1–C8 12 each, C9 18, C10 9, C11 18, C12 5 rows, C13 2 rows, C14 38, C15 11, C16 22', () => {
+    for (const n of ['C1', 'C2', 'C3', 'C4', 'C5', 'C6', 'C7', 'C8']) expect(count(n)).toBe(12);
+    expect(count('C9')).toBe(18);
+    expect(count('C10')).toBe(9);
+    expect(count('C11')).toBe(18);
+    expect(count('C12')).toBe(5);
+    expect(count('C13')).toBe(2);
+    expect(count('C14')).toBe(38);
+    expect(count('C15')).toBe(11);
+    expect(count('C16')).toBe(22);
+  });
+
+  it('column: P1 230, P2 230, couplers 368, P3 38, P5 19, P4 8, P6 32', () => {
+    expect(count('P1')).toBe(230);
+    expect(count('P2')).toBe(230);
+    expect(count('커플러')).toBe(368);
+    expect(count('P3')).toBe(38);
+    expect(count('P5')).toBe(19);
+    expect(count('P4')).toBe(8);
+    expect(count('P6')).toBe(32);
+  });
+
+  it('footing: B1–B4 31 each, B5–B8 40 each, B10-1 18, B10-2 18, B11 60, B12 47', () => {
+    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);
+    expect(count('B10-1')).toBe(18);
+    expect(count('B10-2')).toBe(18);
+    expect(count('B11')).toBe(60);
+    expect(count('B12')).toBe(47);
+  });
+
+  it('warnings: B2 needs a splice (13646 > 12000), and B9 is not computed yet', () => {
+    expect(warnings.map((w) => w.code)).toEqual(expect.arrayContaining(['RB-F08', 'RB-F09']));
+    expect(rows.find((r) => r.name === 'B2')!.length!).toBeGreaterThan(12000);
+  });
+});