Replace device names with serial numbers in MergerFS pool display

Updates disk collector and dashboard to show drive serial numbers
instead of device names (sdX) for MergerFS data/parity drives.
Agent extracts serial numbers from SMART data and dashboard
displays them when available, falling back to device names.

agent/src/collectors/disk.rs

@@ -437,12 +437,14 @@ impl DiskCollector {
             // Return unknown data rather than failing completely
             return Ok(SmartData {
                 health: "UNKNOWN".to_string(),
+                serial_number: None,
                 temperature_celsius: None,
                 wear_percent: None,
             });
         }
         
         let mut health = "UNKNOWN".to_string();
+        let mut serial_number = None;
         let mut temperature = None;
         let mut wear_percent = None;
 
@@ -455,6 +457,15 @@ impl DiskCollector {
                 }
             }
             
+            // Serial number parsing
+            if line.starts_with("Serial Number:") {
+                if let Some(serial_part) = line.split("Serial Number:").nth(1) {
+                    if let Some(serial_str) = serial_part.split_whitespace().next() {
+                        serial_number = Some(serial_str.to_string());
+                    }
+                }
+            }
+            
             // Temperature parsing for different drive types
             if line.contains("Temperature_Celsius") || line.contains("Airflow_Temperature_Cel") {
                 // Traditional SATA drives: attribute table format
@@ -497,6 +508,7 @@ impl DiskCollector {
 
         Ok(SmartData {
             health,
+            serial_number,
             temperature_celsius: temperature,
             wear_percent,
         })
@@ -587,6 +599,7 @@ impl DiskCollector {
             
             cm_dashboard_shared::PoolDriveData {
                 name: d.name.clone(),
+                serial_number: smart.and_then(|s| s.serial_number.clone()),
                 temperature_celsius: temperature,
                 health,
                 wear_percent: smart.and_then(|s| s.wear_percent),
@@ -611,6 +624,7 @@ impl DiskCollector {
             
             cm_dashboard_shared::PoolDriveData {
                 name: d.name.clone(),
+                serial_number: smart.and_then(|s| s.serial_number.clone()),
                 temperature_celsius: temperature,
                 health,
                 wear_percent: smart.and_then(|s| s.wear_percent),
@@ -808,6 +822,7 @@ impl Collector for DiskCollector {
 #[derive(Debug, Clone)]
 struct SmartData {
     health: String,
+    serial_number: Option<String>,
     temperature_celsius: Option<f32>,
     wear_percent: Option<f32>,
 }