feat(01-01): NestJS API with health endpoint and Prisma schema

- NestJS app with ConfigModule and HealthModule
- GET /health endpoint returning {status, timestamp} using HealthResponse type
- Prisma schema with PostgreSQL datasource and Tenant model (multi-tenancy foundation)
- Multi-stage Dockerfile with non-root nestjs user, monorepo root as build context
- Workspace dependency on @tessera/shared for shared types
- Type-check passes successfully

apps/api/package.json

@@ -0,0 +1,28 @@
+{
+  "name": "@tessera/api",
+  "version": "0.0.1",
+  "private": true,
+  "scripts": {
+    "build": "nest build",
+    "start": "node dist/main.js",
+    "start:dev": "nest start --watch",
+    "type-check": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@nestjs/core": "^11.0.0",
+    "@nestjs/common": "^11.0.0",
+    "@nestjs/platform-express": "^11.0.0",
+    "@nestjs/config": "^4.0.0",
+    "rxjs": "^7.0.0",
+    "reflect-metadata": "^0.2.0",
+    "@prisma/client": "^6.0.0",
+    "@tessera/shared": "workspace:*"
+  },
+  "devDependencies": {
+    "prisma": "^6.0.0",
+    "@nestjs/cli": "^11.0.0",
+    "typescript": "^5.5.0",
+    "@types/node": "^22.0.0",
+    "@types/express": "^5.0.0"
+  }
+}