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/Cargo.toml

@@ -21,3 +21,4 @@ tokio = { version = "1.0", features = ["full", "process"] }
 futures = "0.3"
 rand = "0.8"
 gethostname = "0.4"
+lettre = { version = "0.11", default-features = false, features = ["smtp-transport", "builder"] }