fix: 批量匹配日志开始/结束时间相同问题

- "开始时间"改用 created_at（HTTP 请求触发时即记录，早于后台任务）
  避免 0 配对任务中 started_at 与 completed_at 在同一秒内赋值显示相同
- 新增"耗时"列：自动计算 created_at → completed_at 差值并格式化
  (< 1 秒 / X 秒 / X 分 Y 秒)，直观反映任务运行时长
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/MatchingPage.tsx

@@ -29,6 +29,15 @@ import type { MatchingResult } from '../types/matching'
 
 const PAGE_SIZE = 10
 
+function formatDuration(start?: string, end?: string): string {
+  if (!start || !end) return '—'
+  const ms = new Date(end).getTime() - new Date(start).getTime()
+  if (ms < 0) return '—'
+  if (ms < 1000) return '< 1 秒'
+  if (ms < 60000) return `${Math.round(ms / 1000)} 秒`
+  return `${Math.floor(ms / 60000)} 分 ${Math.round((ms % 60000) / 1000)} 秒`
+}
+
 const JOB_STATUS_MAP: Record<string, { label: string; color: 'default' | 'info' | 'warning' | 'success' | 'error' }> = {
   pending: { label: '待启动', color: 'default' },
   running: { label: '运行中', color: 'info' },
@@ -310,8 +319,9 @@ export function MatchingPage() {
                       <TableCell>状态</TableCell>
                       <TableCell>进度</TableCell>
                       <TableCell>触发人</TableCell>
-                      <TableCell>开始时间</TableCell>
-                      <TableCell>结束时间</TableCell>
+                      <TableCell>触发时间</TableCell>
+                      <TableCell>完成时间</TableCell>
+                      <TableCell>耗时</TableCell>
                     </TableRow>
                   </TableHead>
                   <TableBody>
@@ -364,7 +374,7 @@ export function MatchingPage() {
                             </TableCell>
                             <TableCell>
                               <Typography variant="caption" color="text.secondary">
-                                {job.started_at ? new Date(job.started_at).toLocaleString('zh-CN') : '—'}
+                                {new Date(job.created_at).toLocaleString('zh-CN')}
                               </Typography>
                             </TableCell>
                             <TableCell>
@@ -372,10 +382,15 @@ export function MatchingPage() {
                                 {job.completed_at ? new Date(job.completed_at).toLocaleString('zh-CN') : '—'}
                               </Typography>
                             </TableCell>
+                            <TableCell>
+                              <Typography variant="caption" color="text.secondary">
+                                {formatDuration(job.created_at, job.completed_at)}
+                              </Typography>
+                            </TableCell>
                           </TableRow>
                           {hasError && (
                             <TableRow key={`${job.id}-err`}>
-                              <TableCell colSpan={7} sx={{ py: 0 }}>
+                              <TableCell colSpan={8} sx={{ py: 0 }}>
                                 <Collapse in={isExpanded}>
                                   <Box sx={{ p: 1.5, bgcolor: 'grey.50', borderRadius: 1, my: 0.5 }}>
                                     <Typography