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>

server/package.json

@@ -0,0 +1,20 @@
+{
+  "name": "birthday-reminder-server",
+  "version": "1.0.0",
+  "description": "生日提醒小程序自建后端",
+  "main": "src/index.js",
+  "scripts": {
+    "start": "node src/index.js",
+    "dev": "node --watch src/index.js"
+  },
+  "dependencies": {
+    "axios": "^1.7.7",
+    "better-sqlite3": "^11.3.0",
+    "dotenv": "^16.4.5",
+    "express": "^4.21.0",
+    "node-cron": "^3.0.3"
+  },
+  "engines": {
+    "node": ">=18"
+  }
+}