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.

dashboard/src/ui/widgets/system.rs

@@ -311,8 +311,9 @@ impl SystemWidget {
                     Status::Unknown
                 };
                 
+                let display_name = drive.serial_number.clone().unwrap_or(drive.name.clone());
                 let storage_drive = StorageDrive {
-                    name: drive.name.clone(),
+                    name: display_name,
                     temperature: drive.temperature_celsius,
                     wear_percent: drive.wear_percent,
                     status: drive_status,
@@ -333,8 +334,9 @@ impl SystemWidget {
                     Status::Unknown
                 };
                 
+                let display_name = drive.serial_number.clone().unwrap_or(drive.name.clone());
                 let storage_drive = StorageDrive {
-                    name: drive.name.clone(),
+                    name: display_name,
                     temperature: drive.temperature_celsius,
                     wear_percent: drive.wear_percent,
                     status: drive_status,