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

@@ -1,13 +1,5 @@
 import { ApiProperty, ApiPropertyOptional } from "@nestjs/swagger";
-import {
-  IsIn,
-  IsInt,
-  IsNotEmpty,
-  IsOptional,
-  IsString,
-  Min,
-} from "class-validator";
-import { StepType } from "../scenario-step.entity";
+import { IsInt, IsNotEmpty, IsOptional, IsString, Min } from "class-validator";
 
 export class CreateScenarioStepDto {
   @ApiPropertyOptional({ example: "Check login page title" })
@@ -20,12 +12,9 @@ export class CreateScenarioStepDto {
   @Min(0)
   order: number;
 
-  @ApiProperty({ enum: ["login", "exec", "sign"], example: "exec" })
-  @IsIn(["login", "exec", "sign"])
-  type: StepType;
-
   @ApiPropertyOptional({
-    description: "Session name (deprecated — browser is created automatically per run).",
+    description:
+      "Session name (deprecated — browser is created automatically per run).",
     example: "my-session",
   })
   @IsOptional()