simplify: 移除 leader lock，单实例无需分布式锁

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/service/wire.go

@@ -287,10 +287,9 @@ func ProvideScheduledTestRunnerService(
 	planRepo ScheduledTestPlanRepository,
 	scheduledSvc *ScheduledTestService,
 	accountTestSvc *AccountTestService,
-	locker LeaderLocker,
 	cfg *config.Config,
 ) *ScheduledTestRunnerService {
-	svc := NewScheduledTestRunnerService(planRepo, scheduledSvc, accountTestSvc, locker, cfg)
+	svc := NewScheduledTestRunnerService(planRepo, scheduledSvc, accountTestSvc, cfg)
 	svc.Start()
 	return svc
 }