feat(scenario): add scenario runs, run steps, and step ordering

- 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

src/scenario/scenario-step.entity.ts

@@ -25,6 +25,9 @@ export class ScenarioStepEntity {
   @JoinColumn({ name: 'scenarioId' })
   scenario: ScenarioEntity;
 
+  @Column({ default: 0 })
+  order: number;
+
   @Column({ type: 'text' })
   type: StepType;