feat(phase2): 타로 셔플·reference 순수 유틸 + 테스트

Fisher-Yates 셔플, 카드 픽 생성, 참고 블록/메타데이터 빌더 구현.
Task 4(interpret API)·Task 6(UI)에서 소비됨.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/__tests__/tarot-reference.test.ts

@@ -0,0 +1,28 @@
+import { describe, it, expect } from 'vitest';
+import { buildReferenceBlock, buildContextMeta } from '../tarot/reference';
+import { findCard } from '../tarot/cards';
+
+const picks = [
+  { card: findCard('the-fool')!, position: '과거', reversed: false },
+  { card: findCard('the-magician')!, position: '현재', reversed: true },
+  { card: findCard('the-high-priestess')!, position: '미래', reversed: false },
+];
+
+describe('buildReferenceBlock', () => {
+  it('각 카드의 위치·정역·키워드·의미를 텍스트 블록으로 만든다', () => {
+    const block = buildReferenceBlock(picks);
+    expect(block).toContain('과거');
+    expect(block).toContain('The Fool');
+    expect(block).toContain('정방향');
+    expect(block).toContain('역방향');
+    expect(block.length).toBeGreaterThan(50);
+  });
+});
+describe('buildContextMeta', () => {
+  it('메이저 비율·원소 분포·정역 흐름을 계산한다', () => {
+    const meta = buildContextMeta(picks);
+    expect(meta.major_minor_ratio).toBe('3:0');
+    expect(meta.orientation_flow).toBe('upright→reversed→upright');
+    expect(typeof meta.element_distribution).toBe('object');
+  });
+});

lib/__tests__/tarot-shuffle.test.ts

@@ -0,0 +1,20 @@
+import { describe, it, expect } from 'vitest';
+import { fisherYates, buildShuffle } from '../tarot/shuffle';
+import { TAROT_DECK } from '../tarot/cards';
+
+describe('fisherYates', () => {
+  it('원본을 변형하지 않고 같은 원소 집합을 반환한다', () => {
+    const input = [1, 2, 3, 4, 5];
+    const out = fisherYates(input);
+    expect(input).toEqual([1, 2, 3, 4, 5]);
+    expect([...out].sort()).toEqual([1, 2, 3, 4, 5]);
+  });
+});
+describe('buildShuffle', () => {
+  it('요청한 수만큼, 중복 없이, reversed 필드를 갖고 반환한다', () => {
+    const out = buildShuffle(TAROT_DECK, 20);
+    expect(out).toHaveLength(20);
+    expect(new Set(out.map((c) => c.slug)).size).toBe(20);
+    for (const c of out) expect(typeof c.reversed).toBe('boolean');
+  });
+});