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/app.module.ts

@@ -0,0 +1,53 @@
+import { Module } from "@nestjs/common";
+import { ConfigModule, ConfigService } from "@nestjs/config";
+import { AppConfig, validateAppConfig } from "./config/app.config";
+import { TypeOrmModule } from "@nestjs/typeorm";
+import { ScheduleModule } from "@nestjs/schedule";
+import { HealthModule } from "./health/health.module";
+import { AuthModule } from "./auth/auth.module";
+import { BrowserModule } from "./browser/browser.module";
+import { SessionEntity } from "./session/session.entity";
+import { EnvironmentEntity } from "./environment/environment.entity";
+import { EnvironmentModule } from "./environment/environment.module";
+import { McpModule } from "./mcp/mcp.module";
+import { ScenarioEntity } from "./scenario/scenario.entity";
+import { ScenarioStepEntity } from "./scenario/scenario-step.entity";
+import { ScenarioRunEntity } from "./scenario/scenario-run.entity";
+import { ScenarioRunStepEntity } from "./scenario/scenario-run-step.entity";
+import { ScenarioRunLogEntity } from "./scenario/scenario-run-log.entity";
+import { ScenarioModule } from "./scenario/scenario.module";
+
+@Module({
+  imports: [
+    ConfigModule.forRoot({
+      isGlobal: true,
+      envFilePath: ".env",
+      validate: validateAppConfig,
+    }),
+    ScheduleModule.forRoot(),
+    TypeOrmModule.forRootAsync({
+      inject: [ConfigService],
+      useFactory: (config: ConfigService<AppConfig, true>) => ({
+        type: "better-sqlite3",
+        database: config.get("DB_PATH"),
+        entities: [
+          SessionEntity,
+          EnvironmentEntity,
+          ScenarioEntity,
+          ScenarioStepEntity,
+          ScenarioRunEntity,
+          ScenarioRunStepEntity,
+          ScenarioRunLogEntity,
+        ],
+        synchronize: true,
+      }),
+    }),
+    AuthModule,
+    BrowserModule,
+    EnvironmentModule,
+    ScenarioModule,
+    McpModule,
+    HealthModule,
+  ],
+})
+export class AppModule {}