feat: scaffold center and guild backend NestJS skeletons

Fabric.Backend.Center/src/common/health.controller.ts

@@ -0,0 +1,9 @@
+import { Controller, Get } from '@nestjs/common';
+
+@Controller('healthz')
+export class HealthController {
+  @Get()
+  get() {
+    return { ok: true, service: 'center' };
+  }
+}