Implement comprehensive status calculation and notification system

Agent Changes:
• Add CPU status thresholds (warning: ≥5.0, critical: ≥8.0)
• Add memory status thresholds (warning: ≥80%, critical: ≥95%)
• Add service status calculation (critical if failed>0, warning if degraded>0)
• All collectors now calculate and include status in output

Dashboard Changes:
• Update system widget to use agent-calculated cpu_status and memory_status
• Update services widget to use agent-calculated services_status
• Remove client-side status calculations in favor of agent status
• Add status_level_from_agent_status helper function

Notification System:
• Add SMTP email notification system using lettre crate
• Auto-configure notifications: hostname@cmtec.se → cm@cmtec.se
• Smart change detection with rate limiting (30min cooldown)
• Only notify on transitions to/from warning/critical states
• Rich email formatting with host, component, metric details

agent/src/main.rs

@@ -9,6 +9,7 @@ mod agent;
 mod collectors;
 mod config;
 mod discovery;
+mod notifications;
 mod scheduler;
 
 use agent::MetricsAgent;