- install @nestjs/schedule and register ScheduleModule in AppModule
- add ScenarioSchedulerService with two 1s interval jobs:
- activatePendingRuns: flips pending runs to in_progress
- processPendingStepRuns: executes next pending step run (login or exec),
runs optional validateCode, advances or fails the run accordingly
- on step pass: next waiting step becomes pending; last step pass flips run to pass
- on step fail: remaining steps set to cancelled, run flipped to fail
- add cancelled to RunStepStatus union
- add GET /scenarios/:id/runs with pagination and optional ?status= filter