feat(stock): 관심종목 탭 순수 헬퍼(watchlistUtils) + 테스트

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UHXzpsZQxKG9hQmNRfZjRS

src/pages/stock/watchlistUtils.js

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+/* ── 관심종목 탭 순수 헬퍼 (라벨/색/시간) ── */
+
+export const KIND_META = {
+  buy:  { label: '매수', color: '#22c55e', bg: 'rgba(34,197,94,0.12)' },
+  sell: { label: '매도', color: '#ef4444', bg: 'rgba(239,68,68,0.12)' },
+};
+
+const FALLBACK_KIND = { color: '#94a3b8', bg: 'rgba(148,163,184,0.12)' };
+
+export const kindMeta = (kind) => {
+  const meta = KIND_META[kind];
+  if (meta) return meta;
+  return { ...FALLBACK_KIND, label: kind ?? '' };
+};
+
+export const CONDITION_LABEL = {
+  buy_ma20_pullback: 'MA20 눌림 반등',
+  buy_breakout: '박스 상단 돌파',
+  buy_rsi_bounce: 'RSI 과매도 반등',
+  sell_stop_loss: '손절 라인',
+  sell_ma_break: '이평선 이탈',
+  sell_take_profit: '목표가 도달',
+  sell_climax: '과열 소진',
+  sell_trailing_stop: '트레일링 스톱',
+};
+
+export const conditionLabel = (cond) => CONDITION_LABEL[cond] ?? cond ?? '';
+
+export const normalizeTicker = (str) => String(str ?? '').trim();
+
+export const relativeTime = (iso, now = Date.now()) => {
+  if (!iso) return '';
+  const then = new Date(iso).getTime();
+  if (Number.isNaN(then)) return '';
+  const diffMs = now - then;
+  if (diffMs < 0) return '방금';
+  const sec = Math.floor(diffMs / 1000);
+  if (sec < 60) return '방금';
+  const min = Math.floor(sec / 60);
+  if (min < 60) return `${min}분 전`;
+  const hr = Math.floor(min / 60);
+  if (hr < 24) return `${hr}시간 전`;
+  const day = Math.floor(hr / 24);
+  if (day === 1) return '어제';
+  if (day < 7) return `${day}일 전`;
+  return new Date(iso).toLocaleDateString('ko-KR');
+};