Feature/issues 1009 998 986 984

[UG001]

feat: implement API key rotation, rate limiting, ES connection pooling, and typed event bus

• Implement API key rotation with grace period #1009 — API key rotation with grace period
  Add ApiKeyRotationService with dual-key acceptance window, automatic
  expiry, rotation history, domain event emission, and Prometheus metrics.
  Portal facade maps internal types to developer-portal ApiKey type.

• Implement rate limiting with token bucket algorithm #998 — Rate limiting with token bucket algorithm
  Add Express/Fastify rateLimitMiddleware wrapping RateLimitingService.
  Sets X-RateLimit-* headers, handles per-key and per-user windows,
  returns 429 with Retry-After, supports bypass list and IP fallback.

• Implement database connection pooling with optimization #986 — Database connection pooling with optimization
  Add ElasticsearchConnectionPool: fixed-size pool, acquire/release with
  timeout, idle teardown, leak detection, DNS cache with TTL, round-robin
  read-replica routing, tuning recommendations, and Prometheus metrics.
  Extend ElasticsearchConfig with pool settings and env var wiring.

• Refactor event system to use typed event bus with domain events #984 — Typed event bus with domain events
  Add eventBusIntegration.ts wiring backend services to the shared
  EventBus. Domain publishers for subscription, billing, analytics, and
  contract events. DomainEventRouter for cross-domain routing rules.
  Unit tests cover publish/subscribe, wildcard, predicate filters,
  event sourcing replay, SpyEventBus, and EventCollector.
  closes Implement rate limiting with token bucket algorithm #998
  closes Implement database connection pooling with optimization #986
  closes Refactor event system to use typed event bus with domain events #984
  closes Implement API key rotation with grace period #1009

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