…ing.cpp (#356)

* feat(health): implement health monitoring API for test_health_monitoring.cpp

Implement comprehensive health monitoring API as defined in Issue #330:

- health_check: Abstract base class for health checks with get_name(),
  get_type(), check(), get_timeout(), and is_critical() methods
- composite_health_check: Aggregates multiple health checks with
  configurable all-required or any-required semantics
- health_dependency_graph: DAG structure for health check dependencies
  with cycle detection, topological sort, failure impact analysis
- health_check_builder: Builder pattern for creating functional health
  checks with fluent API
- health_monitor: Extended with register_check(), unregister_check(),
  check(), add_dependency(), start()/stop(), get_stats(), get_health_report()
- health_monitor_stats: Statistics tracking for health monitoring
- global_health_monitor(): Singleton accessor for global health monitor

All 22 tests in test_health_monitoring.cpp pass successfully.

Closes #330

* docs: update documentation for health monitoring API

- Add health monitoring API entry to CHANGELOG.md and CHANGELOG_KO.md
- Update KNOWN_ISSUES.md:
  - Remove test_health_monitoring.cpp from disabled tests
  - Add test_health_monitoring.cpp to recently enabled tests
  - Add Health Monitor to API stability table as Stable

* fix(health): resolve thread safety issues in health_monitor

- Change shared_lock to lock_guard in check(), check_all(), and refresh()
  methods since they modify cached_results_ and stats_
- Add missing <condition_variable> header required for cv_ member
- Add thread-safe status handling in test_health_check with atomic status
  and mutex protection for message member
- Add <atomic> and <mutex> headers to test file

Fixes thread sanitizer and undefined behavior sanitizer failures:
- HealthMonitoringTest.HealthMonitorOverallStatus
- HealthMonitoringTest.HealthMonitorStats
- HealthMonitoringTest.HealthMonitorReport
- HealthMonitoringTest.ConcurrentHealthChecks

* docs: add thread safety fix to changelog

Document the health_monitor thread safety fixes in both English and
Korean CHANGELOG files for PR #356.