feat(api): host-agent protocol v2 consumer — heartbeat persistence, auto-register, staleness sweep

Nothing persisted agent heartbeats before: companion_last_seen was
written once at setup and connection_status stayed 'connected' forever.
HostAgentConsumerService now consumes corrosion.*.host.heartbeat
(updates last_seen + status, auto-creates the bare_metal connection row
on first contact), host.going_offline (graceful offline), and sweeps
connections offline after 180s of heartbeat silence. License-existence
tenant validation with caching per NATS-consumer doctrine. WS bridge
forwards host_heartbeat/host_going_offline to the panel.

Contract-verified against production NATS with the backend's own nats
lib: v2 subjects, schema 2, real telemetry, offline beacon.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend-nest/src/app.module.ts

@@ -49,6 +49,9 @@ import { EarlyAccessModule } from './modules/early-access/early-access.module';
 // Shared Services
 import { NatsService } from './services/nats.service';
 import { NatsBridgeService } from './services/nats-bridge.service';
+import { HostAgentConsumerService } from './services/host-agent-consumer.service';
+import { ServerConnection } from './entities/server-connection.entity';
+import { License } from './entities/license.entity';
 import { SteamService } from './services/steam.service';
 
 // Gateway
@@ -91,6 +94,9 @@ import { NatsBridgeGateway } from './gateways/nats-bridge.gateway';
     // Scheduler
     ScheduleModule.forRoot(),
 
+    // Repositories for app-level shared services (host-agent consumer)
+    TypeOrmModule.forFeature([ServerConnection, License]),
+
     // Feature Modules
     AuthModule,
     UsersModule,
@@ -134,6 +140,7 @@ import { NatsBridgeGateway } from './gateways/nats-bridge.gateway';
     // Shared services
     NatsService,
     NatsBridgeService,
+    HostAgentConsumerService,
     SteamService,
 
     // WebSocket gateway