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/tsconfig.json

@@ -0,0 +1,14 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "module": "commonjs",
+    "moduleResolution": "node",
+    "target": "ES2021",
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "emitDecoratorMetadata": true,
+    "experimentalDecorators": true
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}