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

package.json

@@ -0,0 +1,25 @@
+{
+  "name": "mp-pilates",
+  "private": true,
+  "scripts": {
+    "dev:server": "pnpm --filter @mp-pilates/server dev",
+    "dev:app": "pnpm --filter @mp-pilates/app dev:mp-weixin",
+    "build:shared": "pnpm --filter @mp-pilates/shared build",
+    "build:server": "pnpm --filter @mp-pilates/server build",
+    "build:app": "pnpm --filter @mp-pilates/app build:mp-weixin",
+    "test": "pnpm -r test",
+    "lint": "pnpm -r lint"
+  },
+  "engines": {
+    "node": ">=18",
+    "pnpm": ">=8"
+  },
+  "pnpm": {
+    "onlyBuiltDependencies": [
+      "@nestjs/core",
+      "@prisma/client",
+      "@prisma/engines",
+      "prisma"
+    ]
+  }
+}