feat: initial commit - oncology literature search platform

OncoLit: a multi-tenant oncology literature search, feed, and
collaboration platform. Built with FastAPI + Vue 3 + PostgreSQL.
Includes PubMed pipeline, drug approvals, AI summaries, and
systematic review tools.

frontend/src/utils/date.ts

@@ -0,0 +1,39 @@
+/**
+ * 将 UTC ISO 字符串转换为北京时间（UTC+8）的日期/日期时间字符串
+ */
+
+const BJ_OFFSET = 8 * 60 * 60 * 1000 // UTC+8
+
+function _parse(iso: string | null | undefined): Date | null {
+  if (!iso) return null
+  const d = new Date(iso)
+  return isNaN(d.getTime()) ? null : d
+}
+
+/** "2026-07-11" */
+export function toBeijingDate(iso: string | null | undefined): string {
+  const d = _parse(iso)
+  if (!d) return ''
+  return new Date(d.getTime() + BJ_OFFSET).toISOString().slice(0, 10)
+}
+
+/** "2026-07-11 20:30" */
+export function toBeijingDateTime(iso: string | null | undefined): string {
+  const d = _parse(iso)
+  if (!d) return ''
+  return new Date(d.getTime() + BJ_OFFSET).toISOString().slice(0, 16).replace('T', ' ')
+}
+
+/** "2026-07-11 20:30" （别名） */
+export const formatDateTime = toBeijingDateTime
+
+/** 相对时间：刚刚 / N 分钟前 / N 小时前 / N 天前 */
+export function relativeTime(iso: string | null | undefined): string {
+  if (!iso) return ''
+  const diff = Math.floor((Date.now() - new Date(iso).getTime()) / 1000)
+  if (diff < 60) return '刚刚'
+  if (diff < 3600) return `${Math.floor(diff / 60)} 分钟前`
+  if (diff < 86400) return `${Math.floor(diff / 3600)} 小时前`
+  if (diff < 2592000) return `${Math.floor(diff / 86400)} 天前`
+  return iso.slice(0, 10)
+}