feat: Complete NestJS backend scaffold — 22 modules, 39 entities, WebSocket gateway

Full backend rewrite from Rust/Axum to NestJS/TypeScript.
- 22 feature modules (auth, servers, wipes, maps, plugins, players, console,
  chat, team, notifications, settings, schedules, analytics, alerts, status,
  store, webstore, admin, setup, migration, users, licenses)
- 39 TypeORM entities matching PostgreSQL schema (12 migrations)
- Common infrastructure: JWT/RBAC guards, decorators, exception filter
- NATS service with pub/sub/request-reply
- Socket.IO WebSocket gateway with NATS bridge
- Docker: NestJS Dockerfile + updated docker-compose.yml
- Zero compile errors (npx tsc --noEmit clean)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-nest/src/entities/host-billing-record.entity.ts

@@ -0,0 +1,31 @@
+import { Entity, PrimaryGeneratedColumn, Column, ManyToOne, JoinColumn, Unique } from 'typeorm';
+import { Host } from './host.entity';
+
+@Entity('host_billing_records')
+@Unique(['host_id', 'billing_month'])
+export class HostBillingRecord {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @Column({ type: 'uuid' })
+  host_id: string;
+
+  @Column({ type: 'date' })
+  billing_month: Date;
+
+  @Column({ type: 'integer' })
+  active_license_count: number;
+
+  @Column({ type: 'decimal', precision: 10, scale: 2 })
+  wholesale_rate_usd: number;
+
+  @Column({ type: 'decimal', precision: 10, scale: 2 })
+  total_amount_usd: number;
+
+  @Column({ type: 'timestamptz', default: () => 'NOW()' })
+  generated_at: Date;
+
+  @ManyToOne(() => Host, { onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'host_id' })
+  host: Host;
+}