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.

agent/src/collectors/memory.rs

@@ -1,5 +1,5 @@
 use async_trait::async_trait;
-use cm_dashboard_shared::{AgentData, TmpfsData, HysteresisThresholds};
+use cm_dashboard_shared::{AgentData, TmpfsData, HysteresisThresholds, Status};
 
 use tracing::debug;
 
@@ -187,6 +187,11 @@ impl MemoryCollector {
             "/tmp" | "/var/tmp" | "/dev/shm" | "/run" | "/var/log"
         ) || mount_point.starts_with("/run/user/") // User session tmpfs
     }
+
+    /// Calculate memory usage status based on thresholds
+    fn calculate_memory_status(&self, usage_percent: f32) -> Status {
+        self.usage_thresholds.evaluate(usage_percent)
+    }
 }
 
 #[async_trait]
@@ -215,6 +220,9 @@ impl Collector for MemoryCollector {
             );
         }
 
+        // Calculate status using thresholds
+        agent_data.system.memory.usage_status = self.calculate_memory_status(agent_data.system.memory.usage_percent);
+
         Ok(())
     }
 }