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.

shared/src/metrics.rs

@@ -131,6 +131,17 @@ impl HysteresisThresholds {
         }
     }
 
+    /// Evaluate value against thresholds to determine status
+    pub fn evaluate(&self, value: f32) -> Status {
+        if value >= self.critical_high {
+            Status::Critical
+        } else if value >= self.warning_high {
+            Status::Warning
+        } else {
+            Status::Ok
+        }
+    }
+
     pub fn with_custom_gaps(warning_high: f32, warning_gap: f32, critical_high: f32, critical_gap: f32) -> Self {
         Self {
             warning_high,