Display disk serial numbers instead of device names

- Add serial_number field to DriveData structure
- Collect serial numbers from SMART data for all drives
- Display truncated serial numbers (last 8 chars) in dashboard
- Fix parity drive label to show status icon before "Parity:"
- Fix mount point label styling to match other labels

shared/src/agent_data.rs

@@ -66,6 +66,7 @@ pub struct StorageData {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct DriveData {
     pub name: String,
+    pub serial_number: Option<String>,
     pub health: String,
     pub temperature_celsius: Option<f32>,
     pub wear_percent: Option<f32>,