feat: 统一全链路时区为 UTC+8 (Asia/Shanghai)

- schema.sql created_at DEFAULT 改为 datetime(now,+8 hours)
- Dockerfile runtime 安装 tzdata ENV TZ=Asia/Shanghai 并软链 /etc/localtime
- docker-compose.yml 挂载宿主机 localtime 并传 TZ=Asia/Shanghai
- server index.ts 入口设置 process.env.TZ
- client utils/export 新增 utc8Now/utc8Input/utc8DateStamp/utc8DateTimeStamp
- Activities 默认活动开始/结束时间改用 UTC+8
- 导出文件名日期戳和报告生成时间统一 utc8DateStamp/utc8DateTimeStamp

Dockerfile

@@ -16,6 +16,10 @@ FROM node:20-alpine AS runtime
 WORKDIR /app
 ENV NODE_ENV=production
 ENV PORT=3000
+ENV TZ=Asia/Shanghai
+RUN apk add --no-cache tzdata \
+  && ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime \
+  && echo "Asia/Shanghai" > /etc/timezone
 
 COPY server/package.json server/package-lock.json* ./
 RUN npm install --omit=dev --no-audit --no-fund