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/update-scenario.dto.ts

@@ -0,0 +1,10 @@
+import { ApiPropertyOptional } from "@nestjs/swagger";
+import { IsOptional, IsString, IsNotEmpty } from "class-validator";
+
+export class UpdateScenarioDto {
+  @ApiPropertyOptional({ example: "Updated scenario name" })
+  @IsOptional()
+  @IsString()
+  @IsNotEmpty()
+  name?: string;
+}