chore(repo): restructure as monorepo with server and client workspaces

- move NestJS app into server/ subdirectory
- add client/ React+TypeScript (Vite) app with Hello World
- update docker-compose to build and run both services
- add root package.json declaring npm workspaces
- update .gitignore to cover node_modules and dist at all depths

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

@@ -0,0 +1,45 @@
+import { ApiProperty, ApiPropertyOptional } from "@nestjs/swagger";
+import {
+  IsIn,
+  IsInt,
+  IsNotEmpty,
+  IsOptional,
+  IsString,
+  Min,
+} from "class-validator";
+import { StepType } from "../scenario-step.entity";
+
+export class CreateScenarioStepDto {
+  @ApiProperty({ example: 0, description: "Execution order (ascending)" })
+  @IsInt()
+  @Min(0)
+  order: number;
+
+  @ApiProperty({ enum: ["login", "exec", "sign"], example: "exec" })
+  @IsIn(["login", "exec", "sign"])
+  type: StepType;
+
+  @ApiProperty({
+    description:
+      "Session name used by this step. login steps create it; exec steps consume it.",
+    example: "my-session",
+  })
+  @IsString()
+  @IsNotEmpty()
+  sessionName: string;
+
+  @ApiPropertyOptional({ example: "return await page.title();" })
+  @IsOptional()
+  @IsString()
+  @IsNotEmpty()
+  execCode?: string;
+
+  @ApiPropertyOptional({
+    example:
+      'return { success: result !== null, description: "title present" };',
+  })
+  @IsOptional()
+  @IsString()
+  @IsNotEmpty()
+  validateCode?: string;
+}