refactor(scenario): remove step type and simplify scheduler to exec-only

- remove StepType, type column, and type field from step entity and DTOs
- remove executeLoginStep, executeSignStep, executeExecStep from scheduler
- inline exec logic directly in executeStepRun; all steps run execCode
- remove AuthService, EnvironmentService, runEnvironments from scheduler
- remove type selector from CreateStepPage and EditStepPage
- remove type badge column from ScenarioDetailPage
- fix useEffect dependency arrays in RunDetailPage (FINAL, id, runId, polling)
- fix duplicate /snippets proxy key in vite.config.ts
- remove unused escapeHtml export from hljs.ts

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

@@ -9,8 +9,6 @@ import {
 } from "typeorm";
 import { ScenarioEntity } from "./scenario.entity";
 
-export type StepType = "login" | "exec" | "sign";
-
 @Entity("scenario_steps")
 export class ScenarioStepEntity {
   @PrimaryGeneratedColumn("uuid")
@@ -28,9 +26,6 @@ export class ScenarioStepEntity {
   @Column({ default: 0 })
   order: number;
 
-  @Column({ type: "text" })
-  type: StepType;
-
   @Column({ type: "text", nullable: true })
   title: string | null;