Goal: add reliable health/liveness checks and fault isolation baseline for daemon subsystems.

Scope:

• Add HealthStatus model (healthy/degraded/unhealthy)
• Add HealthMonitor service for core components
• Add CircuitBreaker abstraction for LLM/MCP calls
• Expose health summary endpoint/command output

Why now:

• This is the reliability base for BOOT/Cron/Heartbeat/Planner execution.