Implement comprehensive dashboard improvements and maintenance mode

- Storage widget: Restructure with Name/Temp/Wear/Usage columns, SMART details as descriptions
- Host navigation: Only cycle through connected hosts, no disconnected hosts
- Auto-discovery: Skip config files, use predefined CMTEC host list
- Maintenance mode: Suppress notifications during backup via /tmp/cm-maintenance file
- CPU thresholds: Update to warning ≥9.0, critical ≥10.0 for production use
- Agent-dashboard separation: Agent provides descriptions, dashboard displays only

dashboard/src/data/metrics.rs

@@ -21,6 +21,8 @@ pub struct DriveInfo {
     pub available_spare: f32,
     pub capacity_gb: Option<f32>,
     pub used_gb: Option<f32>,
+    #[serde(default)]
+    pub description: Option<Vec<String>>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]