feat(scenario): add scheduler, cancelled step status, and runs list endpoint

- 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

package.json

@@ -19,6 +19,7 @@
     "@nestjs/config": "^4.0.3",
     "@nestjs/core": "^11.1.18",
     "@nestjs/platform-express": "^11.1.18",
+    "@nestjs/schedule": "^6.1.1",
     "@nestjs/swagger": "^11.2.6",
     "@nestjs/typeorm": "^11.0.1",
     "acorn": "^8.16.0",