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/pages/session/SessionsPage.tsx

@@ -4,7 +4,15 @@ import { useTranslation } from 'react-i18next';
 import { Trash2 } from 'lucide-react';
 import { sessions } from '../../api';
 import type { Session } from '../../api';
-import { Badge, Breadcrumbs, Button, Table, type TableColumn, Timestamp, UuidBadge } from '../../ui';
+import {
+  Badge,
+  Breadcrumbs,
+  Button,
+  Table,
+  type TableColumn,
+  Timestamp,
+  UuidBadge,
+} from '../../ui';
 import styles from '../Page.module.css';
 
 export function SessionsPage() {