fix: 日志时区修复 + 日期选择器

- logger.ts: 使用 UTC+8 时区记录日志
- logs.ts: 统计使用 UTC+8 今日日期
- logs.vue: 日期选择器改用 picker 组件
- 移除未使用的 showDatePicker 变量

server/src/routes/logs.ts

@@ -7,6 +7,14 @@ import { requireAdmin } from '../middleware/requireAdmin'
 const router = Router()
 const LOG_DIR = path.resolve(process.env.LOG_DIR || './logs')
 
+/** 获取 UTC+8 今日日期字符串 */
+function getTodayStr(): string {
+  const now = new Date()
+  const utc = now.getTime() + now.getTimezoneOffset() * 60000
+  const d = new Date(utc + 8 * 3600000)
+  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`
+}
+
 /** 获取日志列表（最近7天） */
 router.get('/files', requireAdmin, (_req, res) => {
   try {
@@ -45,8 +53,7 @@ router.get('/stats', requireAdmin, (_req, res) => {
       return res.json({ code: 0, data: { today: { total: 0, errors: 0, slow: 0 }, files: [] } })
     }
 
-    const today = new Date()
-    const dateStr = `${today.getFullYear()}-${String(today.getMonth() + 1).padStart(2, '0')}-${String(today.getDate()).padStart(2, '0')}`
+    const dateStr = getTodayStr()
     const todayFile = path.join(LOG_DIR, `${dateStr}.log`)
 
     let todayStats = { total: 0, errors: 0, slow: 0, warns: 0 }