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/tarot/shuffle.ts

@@ -0,0 +1,18 @@
+import type { TarotCard } from './cards';
+
+export type Pick = { card: TarotCard; position: string; reversed: boolean };
+
+export function fisherYates<T>(input: T[]): T[] {
+  const a = [...input];
+  for (let i = a.length - 1; i > 0; i -= 1) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [a[i], a[j]] = [a[j], a[i]];
+  }
+  return a;
+}
+
+export function buildShuffle(deck: TarotCard[], size: number): (TarotCard & { reversed: boolean })[] {
+  return fisherYates(deck)
+    .slice(0, size)
+    .map((c) => ({ ...c, reversed: Math.random() < 0.5 }));
+}