Repair duration display for bad stopped timestamps (#37121)

Workflow run, job, task, and step durations could show **negative**
values (e.g. `-50s`) when `Stopped` was missing, zero (epoch), or
**before** `Started` (clock skew, races, reruns). The UI used
`calculateDuration` with no validation.

This change:

- Uses each row`s **Updated** timestamp as a **fallback end time** when
`Stopped` is invalid but the status is terminal, so duration
approximates elapsed time instead of `0s` or a negative.
- Keeps **`ActionRun.Duration()`** clamped to **≥ 0** when
`PreviousDuration` plus the current segment would still be negative
(legacy bad data).

Fixes #34582.

Co-authored-by: Composer <composer@cursor.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/actions/run.go

@@ -153,7 +153,11 @@ func (run *ActionRun) LoadRepo(ctx context.Context) error {
 }
 
 func (run *ActionRun) Duration() time.Duration {
-	return calculateDuration(run.Started, run.Stopped, run.Status) + run.PreviousDuration
+	d := calculateDuration(run.Started, run.Stopped, run.Status, run.Updated) + run.PreviousDuration
+	if d < 0 {
+		return 0
+	}
+	return d
 }
 
 func (run *ActionRun) GetPushEventPayload() (*api.PushPayload, error) {