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/dto/create-scenario-step.dto.ts

@@ -10,6 +10,11 @@ import {
 import { StepType } from "../scenario-step.entity";
 
 export class CreateScenarioStepDto {
+  @ApiPropertyOptional({ example: "Check login page title" })
+  @IsOptional()
+  @IsString()
+  title?: string;
+
   @ApiProperty({ example: 0, description: "Execution order (ascending)" })
   @IsInt()
   @Min(0)