接入自建后端 + Gitea CI/CD

- 新增 server/：Node + Express + SQLite + node-cron 实现登录、纪念日 CRUD 和定时订阅消息推送
- 新增 .gitea/workflows/deploy.yml：推送即触发群晖 Docker 部署，监听 15002
- utils/api.js：自动按 envVersion 切换本地/线上 BASE_URL
- app.js 与 add-anniversary.js 移除 wx.cloud 调用，改走自建后端
- cloudfunctions/ 暂保留以便回滚
- 一并提交此前未入库的首页 / 设置页 / 日历 / 万年历等改造

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

utils/date.js

@@ -103,9 +103,28 @@ function parseDate(dateString) {
   return new Date(parseInt(parts[0]), parseInt(parts[1]) - 1, parseInt(parts[2]))
 }
 
+/**
+ * 计算指定月日的下一次发生日期（今年或明年）
+ * @param {Number} month - 月份 (1-12)
+ * @param {Number} day - 日 (1-31)
+ * @returns {{ date: Date, daysUntil: Number }}
+ */
+function getNextOccurrence(month, day) {
+  const today = new Date()
+  const currentYear = today.getFullYear()
+  let date = new Date(currentYear, month - 1, day)
+  let daysUntil = getDaysUntil(date)
+  if (daysUntil < 0) {
+    date = new Date(currentYear + 1, month - 1, day)
+    daysUntil = getDaysUntil(date)
+  }
+  return { date, daysUntil }
+}
+
 module.exports = {
   formatDate,
   getDaysUntil,
+  getNextOccurrence,
   isToday,
   isPast,
   isUpcoming,