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.controller.ts

@@ -0,0 +1,9 @@
+import { Controller, Get } from '@nestjs/common'
+
+@Controller()
+export class AppController {
+  @Get('health')
+  health() {
+    return { status: 'ok', timestamp: new Date().toISOString() }
+  }
+}