- Create CacheStrategyService with Redis-based distributed caching
- Implement cache invalidation on data updates
- Add cache hit/miss metrics tracking
- Support configurable TTL per resource type
- Implement cache warming for critical data
- Add stale-while-revalidate pattern support
- Create CacheInterceptor for automatic GET request caching
- Add CacheConfig decorator for endpoint-level configuration
- Provide cache metrics dashboard

- Implement health indicators for Redis, Email, Soroban RPC, and Horizon
- Add GET /health/detailed endpoint with per-service status
- Track response time metrics for each dependency
- Support degraded state when non-critical services fail
- Add HealthHistoryService for historical health data
- Provide uptime statistics and performance metrics
- Add GET /health/history and GET /health/stats endpoints
- Integration with monitoring tools ready

- Create GracefulShutdownService to manage shutdown lifecycle
- Handle SIGTERM and SIGINT signals properly
- Stop accepting new requests during shutdown
- Wait for in-flight requests to complete (with 25s timeout)
- Close database connections gracefully
- Close Redis connections cleanly
- Add GracefulShutdownInterceptor to track active requests
- Log shutdown process with detailed timing
- Maximum shutdown timeout of 30 seconds
- Handle uncaught exceptions and unhandled rejections

…#488-491