- add ScenarioRunEntity (pending|in_progress|pass|fail) and ScenarioRunStepEntity (waiting|pending|in_progress|pass|fail)
- add POST /scenarios/:id/run — creates run with first step pending, rest waiting
- add order field to ScenarioStepEntity and ScenarioRunStepEntity for deterministic sequential execution
- findOne and createRun now sort steps/stepRuns by order ASC