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/shared/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@mp-pilates/shared",
+  "version": "0.1.0",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "scripts": {
+    "build": "tsc",
+    "dev": "tsc --watch"
+  },
+  "devDependencies": {
+    "typescript": "^5.4.0"
+  }
+}