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

client/src/ui/Textarea/Textarea.tsx

@@ -1,8 +1,10 @@
 import React, { useId } from 'react';
 import styles from './Textarea.module.css';
 
-export interface TextareaProps
-  extends Omit<React.TextareaHTMLAttributes<HTMLTextAreaElement>, 'id'> {
+export interface TextareaProps extends Omit<
+  React.TextareaHTMLAttributes<HTMLTextAreaElement>,
+  'id'
+> {
   label?: string;
   hint?: string;
   error?: string;