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/scenario-step.entity.ts

@@ -0,0 +1,48 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  CreateDateColumn,
+  UpdateDateColumn,
+  ManyToOne,
+  JoinColumn,
+} from "typeorm";
+import { ScenarioEntity } from "./scenario.entity";
+
+export type StepType = "login" | "exec" | "sign";
+
+@Entity("scenario_steps")
+export class ScenarioStepEntity {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column()
+  scenarioId: number;
+
+  @ManyToOne(() => ScenarioEntity, (scenario) => scenario.steps, {
+    onDelete: "CASCADE",
+  })
+  @JoinColumn({ name: "scenarioId" })
+  scenario: ScenarioEntity;
+
+  @Column({ default: 0 })
+  order: number;
+
+  @Column({ type: "text" })
+  type: StepType;
+
+  @Column({ type: "text" })
+  sessionName: string;
+
+  @Column({ type: "text", nullable: true })
+  execCode: string | null;
+
+  @Column({ type: "text", nullable: true })
+  validateCode: string | null;
+
+  @CreateDateColumn()
+  createdAt: Date;
+
+  @UpdateDateColumn()
+  updatedAt: Date;
+}