feat(scenarios): add step title, scenario credentials, and environment context in executor

- add nullable title column to scenario steps; exposed in create/edit forms and step table
- add scenario-credential join (many-to-many with CredentialEntity) with CRUD endpoints
- expose environment URLs in code executor helpers via helpers.env and helpers.getEnvUrl()
- resolve and cache environment per run from the login step's environmentName in scheduler
- add section spacing and step table title column to ScenarioDetailPage

server/src/scenario/scenario-step.entity.ts

@@ -31,6 +31,9 @@ export class ScenarioStepEntity {
   @Column({ type: "text" })
   type: StepType;
 
+  @Column({ type: "text", nullable: true })
+  title: string | null;
+
   @Column({ type: "text" })
   sessionName: string;