Complete monitoring system restoration

Fully restored CM Dashboard as a complete monitoring system with working
status evaluation and email notifications.

COMPLETED PHASES:
✅ Phase 1: Fixed storage display issues
  - Use lsblk instead of findmnt (eliminates /nix/store bind mount)
  - Fixed NVMe SMART parsing (Temperature: and Percentage Used:)
  - Added sudo to smartctl for permissions
  - Consistent filesystem and tmpfs sorting

✅ Phase 2a: Fixed missing NixOS build information
  - Added build_version field to AgentData
  - NixOS collector now populates build info
  - Dashboard shows actual build instead of "unknown"

✅ Phase 2b: Restored status evaluation system
  - Added status fields to all structured data types
  - CPU: load and temperature status evaluation
  - Memory: usage status evaluation
  - Storage: temperature, health, and filesystem usage status
  - All collectors now use their threshold configurations

✅ Phase 3: Restored notification system
  - Status change detection between collection cycles
  - Email alerts on status degradation (OK→Warning/Critical)
  - Detailed notification content with metric values
  - Full NotificationManager integration

CORE FUNCTIONALITY RESTORED:
- Real-time monitoring with proper status evaluation
- Email notifications on threshold violations
- Correct storage display (nvme0n1 T: 28°C W: 1%)
- Complete status-aware infrastructure monitoring
- Dashboard is now a monitoring system, not just data viewer

The CM Dashboard monitoring system is fully operational.

dashboard/src/ui/widgets/system.rs

@@ -138,6 +138,9 @@ impl Widget for SystemWidget {
 
         // Extract agent version
         self.agent_hash = Some(agent_data.agent_version.clone());
+        
+        // Extract build version
+        self.nixos_build = agent_data.build_version.clone();
 
         // Extract CPU data directly
         let cpu = &agent_data.system.cpu;