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

agent/src/collectors/smart.rs

@@ -357,6 +357,8 @@ struct SmartDeviceData {
     health_status: String,
     capacity_gb: Option<f32>,
     used_gb: Option<f32>,
+    #[serde(default)]
+    description: Option<Vec<String>>,
 }
 
 impl SmartDeviceData {
@@ -389,6 +391,21 @@ impl SmartDeviceData {
             })
             .unwrap_or_else(|| "UNKNOWN".to_string());
 
+        // Build SMART description with key metrics
+        let mut smart_details = Vec::new();
+        if available_spare > 0.0 {
+            smart_details.push(format!("Spare: {}%", available_spare as u32));
+        }
+        if power_on_hours > 0 {
+            smart_details.push(format!("Hours: {}", power_on_hours));
+        }
+        
+        let description = if smart_details.is_empty() {
+            None
+        } else {
+            Some(vec![smart_details.join(", ")])
+        };
+
         Self {
             name: device.to_string(),
             temperature_c,
@@ -398,6 +415,7 @@ impl SmartDeviceData {
             health_status,
             capacity_gb: None, // Will be set later by the collector
             used_gb: None,     // Will be set later by the collector
+            description,
         }
     }
 }