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/snippet/snippet.service.ts

@@ -58,7 +58,8 @@ export class SnippetService {
     const snippet = await this.findOne(id);
     if (dto.name && dto.name !== snippet.name) {
       const conflict = await this.repo.findOneBy({ name: dto.name });
-      if (conflict) throw new ConflictException(`Snippet "${dto.name}" already exists`);
+      if (conflict)
+        throw new ConflictException(`Snippet "${dto.name}" already exists`);
     }
     Object.assign(snippet, dto);
     return this.repo.save(snippet);