feat(notifications): production-ready WebSocket gateway (TEC-2766)

- Add RedisIoAdapter (shared/infra) for multi-instance Socket.IO fan-out
  with graceful fallback to the in-memory IoAdapter when Redis is
  unreachable.
- Pin Socket.IO heartbeat (pingInterval/pingTimeout/connectTimeout)
  via env-tunable gateway options for reconnect stability.
- Expose Prometheus metrics on /notifications: goodgo_ws_connected_clients
  (Gauge) and goodgo_ws_messages_total (Counter) with namespace/event/
  direction labels. Wired through MetricsService and tracked across
  connect/disconnect + emits.
- Unit tests: RedisIoAdapter connect/fallback/close, new MetricsService
  WS helpers, and gateway metric increments/decrements on auth paths.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/shared/infrastructure/index.ts

@@ -11,6 +11,7 @@ export {
 export { createEncryptionExtension } from './encryption-middleware';
 export { PrismaService } from './prisma.service';
 export { RedisService } from './redis.service';
+export { RedisIoAdapter } from './redis-io.adapter';
 export { CacheService, CachePrefix, CacheTTL } from './cache.service';
 export { LoggerService } from './logger.service';
 export { EventBusService } from './event-bus.service';