Fail a run whose ai_runs row is saved after the skill timeout

runOnce checked the deadline only before saving the row. The save can
wait for the store's single writer, so a run whose work ended in time
could return success after its timeout. Check the deadline again once
the row is saved and return llm.ErrTimeout when it has passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/ai/harness/harness.go

@@ -186,6 +186,12 @@ func runOnce[In, Out any](ctx context.Context, cfg Config, s Skill[In, Out], tim
 	if err != nil {
 		return zero, err
 	}
+	// The save may wait past the deadline for the store's single writer.
+	// The run has then not ended in time, so it fails, though its row
+	// records the work's outcome as it stood before the save.
+	if !time.Now().Before(deadline) {
+		return zero, expired
+	}
 	return out, nil
 }