feat: scaffold monorepo with shared types and NestJS server

- pnpm workspace with packages/app, packages/server, packages/shared
- @mp-pilates/shared: enums, constants, TypeScript interfaces for all 8 data models
- @mp-pilates/server: NestJS bootstrap with health check, validation pipe, CORS
- Base TypeScript config with strict mode

packages/server/src/app.module.ts

@@ -0,0 +1,14 @@
+import { Module } from '@nestjs/common'
+import { ConfigModule } from '@nestjs/config'
+import { AppController } from './app.controller'
+
+@Module({
+  imports: [
+    ConfigModule.forRoot({
+      isGlobal: true,
+      envFilePath: ['.env.local', '.env'],
+    }),
+  ],
+  controllers: [AppController],
+})
+export class AppModule {}